Eleven: Minor redesign of widgets

* Instead of black and white use some light and dark tones from the
  system accent palette (blatantly stolen the ones from the new
  DigitalAppWidget from DeskClock)
* Increase padding on large / large alternate
* Show default texts and image when there is no music loaded yet (e.g.
  on our default home screen or after a reboot)

Change-Id: I49ca68a1ecff38dfcd318225647299f7c16e0943