Added "Scenes" menu to switch between different scene files.

It works exactly like how the Profile menu works. I see this being useful for keeping the scenes list clean by having different scene files for different things like a scene file with Minecraft related scenes, or for experimenting with new scenes setup without messing up your old scenes setup. 

You can switch between different scene files while streaming.

All scenes are stored in the "scenes" folder.

When obs is updated for existing users their "scenes.xconfig" file will be moved to the "scenes" folder.

Scenes files can be created/renamed/removed in "Settings:General".

Added "Profile: <ProfileName > Scene: <ScenesName>" to the beginning of the app name.