Move gui initialization out of __init__.
Spotimcgui: Settings: Remove dependencies over spotify objects.
Spotimcgui: Settings: Added class for storing global infolabels.
Add support for running in the background.
Merge branch 'master' into background-support
Spotimcgui: Main Window: Don't minimize on exit.
Main Window: Minimize addon when navigating back on a topmost view.

This closes #121.
Main Window: Flush caches when minimizing.