To simplify the playlist handling, enforce that the indices are always
formatted to the same length (5, which allows for 100000 entries, that
should be enough).
Then make the position stored in the Playlist object be a simple integer
instead of a database key. This simplifies the code, and will make
implementing shuffle much easier.
Signed-off-by: Matthias Blankertz <matthias@blankertz.org>
Add documentation of playlist database schema in DEVELOP.md.
Add settings for persist and shuffle to BTreeDB. Implement the different
persist modes. Shuffle will be implemented in a followup commit.
Signed-off-by: Matthias Blankertz <matthias@blankertz.org>
