Turns GameTicker into an EntitySystem. (#4197)

* GameTicker turned into an EntitySystem

* Turns ClientGameTicker into an EntitySystem, turn NetMessages into events

* Change event names to be more consistent with the rest.

* YAML linter uses the dummy gameticker CVar override.

* Fix game ticker initialization order

* Dummy ticker won't spawn players.

* Fix character creation test

Content.Server/Mind/MindHelpers.cs

@@ -14,7 +14,7 @@ namespace Content.Server.Mind
 
             if (mind == null) return;
 
-            IoCManager.Resolve<IGameTicker>().OnGhostAttempt(mind, canReturn);
+            EntitySystem.Get<GameTicker>().OnGhostAttempt(mind, canReturn);
         }
     }
 }