Make gapless playback enabled by default

[deed02392]

Gapless playback appears to be supported and work well. Listening to mixed albums as they are intended to be heard only works when gapless playback is enabled, otherwise there is a >100ms delay between tracks which is very jarring.

Describe the solution you'd like
Enable gapless playback by default

Describe alternatives you've considered

• Enabled when an album is added to the queue, disabled otherwise
• Hotkey to toggle

Additional context
Feature added in #369

[hrkfdn]

I have enabled it by default, I think Spotify does this as well. It's a little crude, but it seems non-trivial to come up with a logic enable it dynamically.