Redo window mode handling

This is an entirely obscene and overly complicated approach, but we must
be able to track what was being viewed before something else, i.e. if
the user is in album mode and decides to open settings.

This ****must**** be redone in the future, and we should consider even
dropping PlayerView, as it's also obscene. Moving to a PlayList concept
makes far more sense, and then we don't have to worry about so much
switching logic (which view should I switch back to?)