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/IoC/ServerContentIoC.cs

@@ -39,7 +39,6 @@ namespace Content.Server.IoC
         {
             IoCManager.Register<ISharedNotifyManager, ServerNotifyManager>();
             IoCManager.Register<IServerNotifyManager, ServerNotifyManager>();
-            IoCManager.Register<IGameTicker, GameTicker>();
             IoCManager.Register<IChatManager, ChatManager>();
             IoCManager.Register<IMoMMILink, MoMMILink>();
             IoCManager.Register<ISandboxManager, SandboxManager>();