[ModernForum] ScreenManager renamed to SceneManager

I like the idea of scenes rather than scenes.. I'm going to run with
this idea for my UI. Influenced by my experience with game engines
[ModernForum] Moved MasterLayoutScreen to Scenes Folder

I wanted to cleanup the Scenes into its own folder in prepartion for
more scenes
[ModernForum] Rename MasterLayoutScreen to MasterLayoutScene

Cleaning up the masterscene name ..