Move Login/loading screen to a optional plugin. Fix IAssetFactory further.

Had some downtime at home and decided to move the login/loading screen stuff to an optional plugin. This was kind of glaring misuse of UiAPI and what it should not have.

The console and taskbar stuff might be next in line to be removed from UiAPI, but those can already be disabled easily `new TundraClient( { taskbar : false, console : false });`