this should significantly reduce CPU usage but is a little bit more complicated.
while we're at it, remove the different screen redraw events and use a combined
event for all screens.
TODO:
the spotify player still needs to update the statusbar at least every second.
this is a pretty big but necessary change and might not be stable yet.
some key points:
- the queue is now responsible for playback controls and track management, as
this was scattered between the queue and spotify objects.
- because the queue is now retained, it should be easier to save it as a
spotify playlist
closes#12
- move from listview to linearlayout + scrollview
- doesn't redraw the whole view on queue changes anymore
- uses new cursive functions for linearlayout (needs cursive git)
closes#3
