Implement album shuffle
Reason for the change
This implements album shuffle.
Test plan
Autotests have been updated and new tests have been added.
Screenshots or screen recordings
| Before (no shuffle) | Before (track shuffle) | After (no shuffle) | After (track shuffle) | After (album shuffle) |
|---|---|---|---|---|
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I took the album shuffle icon from amarok (media-random-albums-amarok). AFAIK this is part of breeze, so should be ok to use, although it is less general than the regular shuffle track icon.
Alternative for track shuffle with be the associated amarok track shuffle icon: 
Or should we ship a dedicated icon with Elisa?
Bugs fixed
This also fixes an unreported (AFAICS) bug: when Elisa would be closed with a shuffled playlist, it would re-open next time with a different randomized playlist with an unrelated other track set to current track. This MR also saves the randomized order of the shuffled tracks, such that on the next startup the playlist and current track are correctly restored.