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/IoC/ClientContentIoC.cs

@@ -33,7 +33,6 @@ namespace Content.Client.IoC
             IoCManager.Register<IGameHud, GameHud>();
             IoCManager.Register<IClientNotifyManager, ClientNotifyManager>();
             IoCManager.Register<ISharedNotifyManager, ClientNotifyManager>();
-            IoCManager.Register<IClientGameTicker, ClientGameTicker>();
             IoCManager.Register<IParallaxManager, ParallaxManager>();
             IoCManager.Register<IChatManager, ChatManager>();
             IoCManager.Register<IEscapeMenuOwner, EscapeMenuOwner>();