Popup message notifications. (#125)

* Popup message system v1

* Networking for the popup notifications.

Ship it.

Content.Shared/SharedNotifyManager.cs

@@ -0,0 +1,48 @@
+using Content.Shared.Interfaces;
+using Lidgren.Network;
+using SS14.Shared.Interfaces.GameObjects;
+using SS14.Shared.Interfaces.Network;
+using SS14.Shared.Map;
+using SS14.Shared.Network;
+using SS14.Shared.Network.Messages;
+
+namespace Content.Shared
+{
+    public abstract class SharedNotifyManager : ISharedNotifyManager
+    {
+        public void PopupMessage(IEntity source, IEntity viewer, string message)
+        {
+            // TODO: we might eventually want for this to pass the actual entity,
+            // so the notify could track the entity movement visually.
+            PopupMessage(source.Transform.LocalPosition, viewer, message);
+        }
+
+        public abstract void PopupMessage(GridLocalCoordinates coordinates, IEntity viewer, string message);
+
+        protected class MsgDoNotify : NetMessage
+        {
+            #region REQUIRED
+
+            public const MsgGroups GROUP = MsgGroups.Command;
+            public const string NAME = nameof(MsgDoNotify);
+            public MsgDoNotify(INetChannel channel) : base(NAME, GROUP) { }
+
+            #endregion
+
+            public string Message { get; set; }
+            public GridLocalCoordinates Coordinates;
+
+            public override void ReadFromBuffer(NetIncomingMessage buffer)
+            {
+                Message = buffer.ReadString();
+                Coordinates = buffer.ReadGridLocalCoordinates();
+            }
+
+            public override void WriteToBuffer(NetOutgoingMessage buffer)
+            {
+                buffer.Write(Message);
+                buffer.Write(Coordinates);
+            }
+        }
+    }
+}