Refactor so that playlists and shows are stored application wide

Currently we store show data in the ShowManager and files and playlist data in the FileManager. This is unhandy, as other components sometimes need access to the same data. Also Shows, Files and Playlists should be all loaded at login and then we can modify only the changed parts inside the components, instead of reloading everything.

Also fix this:

• when switching between ShowManger, FileManager and EmissionManager, keep the same show as the currently active one.