WebView fixes and improvements.

Re-organize initialization so that User-Agent CVar actually works.

Add web.headless CVar to not load CEF even on graphical client.

Clean up init logic to not rely on static IoC, and clean up loggers used too.

Robust.Client/GameController/GameController.cs

@@ -131,6 +131,10 @@ namespace Robust.Client
 
             // Call Init in game assemblies.
             _modLoader.BroadcastRunLevel(ModRunLevel.PreInit);
+
+            // Finish initialization of WebView if loaded.
+            _webViewHook?.Initialize();
+
             _modLoader.BroadcastRunLevel(ModRunLevel.Init);
 
             // Start bad file extensions check after content init,