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/Administration/Commands/ReadyAll.cs

@@ -3,6 +3,7 @@ using Content.Server.GameTicking;
 using Content.Shared.Administration;
 using Robust.Server.Player;
 using Robust.Shared.Console;
+using Robust.Shared.GameObjects;
 using Robust.Shared.IoC;
 
 namespace Content.Server.Administration.Commands
@@ -22,7 +23,7 @@ namespace Content.Server.Administration.Commands
                 ready = bool.Parse(args[0]);
             }
 
-            var gameTicker = IoCManager.Resolve<IGameTicker>();
+            var gameTicker = EntitySystem.Get<GameTicker>();
             var playerManager = IoCManager.Resolve<IPlayerManager>();