FIX jsonifiy a NoneType object in case of failed playlist generation
Merge branch 'dev/solo'
FIX typos
FIX track filtering
Improved cleanup.py, now handles automatic groups.

Improvements to the script `cleanup.py` that cleans up the groups that are
inactive. Now it also takes care of correctly clean up automatic groups.
add groupstreamers features, edit iterative method
Merge branch 'groupSuggestion'