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.Client/GlobalVerbs/ViewVariablesVerb.cs

@@ -0,0 +1,32 @@
+using Content.Shared.GameObjects;
+using Robust.Client.Console;
+using Robust.Client.ViewVariables;
+using Robust.Shared.Interfaces.GameObjects;
+using Robust.Shared.IoC;
+
+namespace Content.Client.GlobalVerbs
+{
+    /// <summary>
+    /// Global verb that opens a view variables window for the entity in question.
+    /// </summary>
+    [GlobalVerb]
+    class ViewVariablesVerb : GlobalVerb
+    {
+        public override string GetText(IEntity user, IEntity target) => "View variables";
+        public override bool RequireInteractionRange => false;
+
+        public override VerbVisibility GetVisibility(IEntity user, IEntity target)
+        {
+            var groupController = IoCManager.Resolve<IClientConGroupController>();
+            if (groupController.CanViewVar())
+                return VerbVisibility.Visible;
+            return VerbVisibility.Invisible;
+        }
+
+        public override void Activate(IEntity user, IEntity target)
+        {
+            var vvm = IoCManager.Resolve<IViewVariablesManager>();
+            vvm.OpenVV(target);
+        }
+    }
+}