Fix bug in mp3.py where list was treated as set

Signed-off-by: Niklas Koep <niklas.koep@gmail.com>
Continue PEP8 compliance fixes

Signed-off-by: Niklas Koep <niklas.koep@gmail.com>
Update menu label when playlist lock state changes

Includes additional PEP8 fixes.

Signed-off-by: Niklas Koep <niklas.koep@gmail.com>