Reset playback on queue end

Related issue: #1380 (closed)

When reaching the end of the playback queue, two things now happen:

• The track progress resets to 0:00 (same as before)
• The playback icon now resets from ⏸️(pause) to ▶️(play) (new)

This Merge Request includes:

• Tests
• A changelog fragment (cf https://docs.funkwhale.audio/contributing.html#changelog-management)