Add global verbs (#400)

* Add support for global verbs

These are verbs that are visible for all entities, regardless of their components. This works by adding a new class `GlobalVerb` and a new attribute `GlobalVerbAttribute`. It works in the same way as current verbs, except you can put the verbs class definition anywhere instead of inside a component. Also moved VerbUtility into it's own file since it now has functions for both verbs and global verbs.

* Add view variables verb as an example of global verbs

* Implement suggested changes

Implemented some suggested changes from code review:
- Remove unneeded attribute from `GlobalVerb`
- Added some useful attributes to `GlobalVerbAttribute`
- Moved constants used by both `Verb` and `GlobalVerb` into `VerbUtility`

* Reduce duplicate code in VerbSystem (client & server)

Greatly reduced the amount of duplicate code for handling component verbs and global verbs separately.

* Update engine submodule

Need this so client side permissions checks are available.

Content.Shared/GameObjects/Verbs/Verb.cs

@@ -0,0 +1,130 @@
+using System;
+using System.Collections.Generic;
+using System.Reflection;
+using JetBrains.Annotations;
+using Robust.Shared.Interfaces.GameObjects;
+using Robust.Shared.Utility;
+
+namespace Content.Shared.GameObjects
+{
+    /// <summary>
+    ///     A verb is an action in the right click menu of an entity.
+    /// </summary>
+    /// <remarks>
+    ///     To add a verb to an entity, define it as a nested class inside the owning component,
+    ///     and mark it with <see cref="VerbAttribute"/>
+    /// </remarks>
+    [UsedImplicitly]
+    public abstract class Verb
+    {
+        /// <summary>
+        ///     If true, this verb requires the user to be inside within
+        ///     <see cref="InteractionRange"/> meters from the entity on which this verb resides.
+        /// </summary>
+        public virtual bool RequireInteractionRange => true;
+
+        /// <summary>
+        ///     Gets the text string that will be shown to <paramref name="user"/> in the right click menu.
+        /// </summary>
+        /// <param name="user">The entity of the user opening this menu.</param>
+        /// <param name="component">The component instance for which this verb is being loaded.</param>
+        /// <returns>The text string that is shown in the right click menu for this verb.</returns>
+        public abstract string GetText(IEntity user, IComponent component);
+
+        /// <summary>
+        ///     Gets the visibility level of this verb in the right click menu.
+        /// </summary>
+        /// <param name="user">The entity of the user opening this menu.</param>
+        /// <param name="component">The component instance for which this verb is being loaded.</param>
+        /// <returns>The visibility level of the verb in the client's right click menu.</returns>
+        public abstract VerbVisibility GetVisibility(IEntity user, IComponent component);
+
+        /// <summary>
+        ///     Invoked when this verb is activated from the right click menu.
+        /// </summary>
+        /// <param name="user">The entity of the user opening this menu.</param>
+        /// <param name="component">The component instance for which this verb is being loaded.</param>
+        public abstract void Activate(IEntity user, IComponent component);
+    }
+
+    /// <inheritdoc />
+    /// <summary>
+    ///     Sub class of <see cref="T:Content.Shared.GameObjects.Verb" /> that works on a specific type of component,
+    ///     to reduce casting boiler plate for implementations.
+    /// </summary>
+    /// <typeparam name="T">The type of component that this verb will run on.</typeparam>
+    public abstract class Verb<T> : Verb where T : IComponent
+    {
+        /// <summary>
+        ///     Gets the text string that will be shown to <paramref name="user"/> in the right click menu.
+        /// </summary>
+        /// <param name="user">The entity of the user opening this menu.</param>
+        /// <param name="component">The component instance for which this verb is being loaded.</param>
+        /// <returns>The text string that is shown in the right click menu for this verb.</returns>
+        protected abstract string GetText(IEntity user, T component);
+
+        /// <summary>
+        ///     Gets the visibility level of this verb in the right click menu.
+        /// </summary>
+        /// <param name="user">The entity of the user opening this menu.</param>
+        /// <param name="component">The component instance for which this verb is being loaded.</param>
+        /// <returns>The visibility level of the verb in the client's right click menu.</returns>
+        protected abstract VerbVisibility GetVisibility(IEntity user, T component);
+
+        /// <summary>
+        ///     Invoked when this verb is activated from the right click menu.
+        /// </summary>
+        /// <param name="user">The entity of the user opening this menu.</param>
+        /// <param name="component">The component instance for which this verb is being loaded.</param>
+        protected abstract void Activate(IEntity user, T component);
+
+        /// <inheritdoc />
+        public sealed override string GetText(IEntity user, IComponent component)
+        {
+            return GetText(user, (T) component);
+        }
+
+        /// <inheritdoc />
+        public sealed override VerbVisibility GetVisibility(IEntity user, IComponent component)
+        {
+            return GetVisibility(user, (T) component);
+        }
+
+        /// <inheritdoc />
+        public sealed override void Activate(IEntity user, IComponent component)
+        {
+            Activate(user, (T) component);
+        }
+    }
+
+    /// <summary>
+    ///     This attribute should be used on <see cref="Verb"/> implementations nested inside component classes,
+    ///     so that they're automatically detected.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Class, Inherited = false)]
+    [MeansImplicitUse]
+    public sealed class VerbAttribute : Attribute
+    {
+    }
+
+    /// <summary>
+    /// Possible states of visibility for the verb in the right click menu.
+    /// </summary>
+    public enum VerbVisibility
+    {
+        /// <summary>
+        /// The verb will be listed in the right click menu.
+        /// </summary>
+        Visible,
+
+        /// <summary>
+        /// The verb will be listed, but it will be grayed out and unable to be clicked on.
+        /// </summary>
+        Disabled,
+
+        /// <summary>
+        /// The verb will not be listed in the right click menu.
+        /// </summary>
+        Invisible
+    }
+}