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.Client/Entry/EntryPoint.cs

@@ -167,7 +167,6 @@ namespace Content.Client.Entry
 
             IoCManager.Resolve<IGameHud>().Initialize();
             IoCManager.Resolve<IClientNotifyManager>().Initialize();
-            IoCManager.Resolve<IClientGameTicker>().Initialize();
 
             var overlayMgr = IoCManager.Resolve<IOverlayManager>();
             overlayMgr.AddOverlay(new ParallaxOverlay());