Gravity fixes (#4231)

git was being dumb so I just made a diff pr

Content.Server/Gravity/EntitySystems/GravitySystem.cs

@@ -56,17 +56,22 @@ namespace Content.Server.Gravity.EntitySystems
         {
             // Incase there's already a generator on the grid we'll just set it now.
             var gridId = component.Owner.Transform.GridID;
+            GravityChangedMessage message;
 
             foreach (var generator in ComponentManager.EntityQuery<GravityGeneratorComponent>(true))
             {
                 if (generator.Owner.Transform.GridID == gridId && generator.Status == GravityGeneratorStatus.On)
                 {
                     component.Enabled = true;
+                    message = new GravityChangedMessage(gridId, true);
+                    RaiseLocalEvent(message);
                     return;
                 }
             }
 
             component.Enabled = false;
+            message = new GravityChangedMessage(gridId, false);
+            RaiseLocalEvent(message);
         }
 
         public override void Update(float frameTime)