diskOS Disco! 2.5.7

Fixes from a code review of 2.5.6, safer Bluetooth recovery, and a Windows installer that always installs the latest
release.

Testing: these fixes were checked with automatic tests and on a computer. They were not yet tried on a Disc,
and Bluetooth AAC/LDAC not at all (no such headphones at hand). Reports are welcome on
issue #13.

Bluetooth

• Safer automatic resume (#13). When Disco moves the sound back
  to your headphones and the song stops by itself, it presses play once. If music still doesn't move, or after an
  AAC/LDAC switch, it shows "Playback paused - press Play to resume" instead of acting. It only watches for a few
  seconds, for the same headphones and song, and never after you press Play/Pause yourself or at the end of a song.
• No more codec blacklist. 2.5.6 could mistake an ordinary pause for a failed AAC/LDAC connection and switch those
  headphones back to SBC for good. That is gone: headphones 2.5.6 moved to SBC can use AAC/LDAC again.

Picking several items

Picking now works with the exact songs for every action (Play, Queue, Add to playlist, Add to Favourites):

• One track of a CUE/ISO album stays one track in the queue, instead of the whole album.
• An album picked under one artist no longer pulls in another artist's album with the same name.
• Folders with CUE/ISO files keep every track; very large albums are no longer cut off at 512 songs.
• Add to Favourites only reports what was really saved, and keeps the selection when something fails.
• Select all in Files only ticks folders and songs.
• Queuing many songs at once is faster (the queue is saved once).

Queue

• A queue start that fails no longer loses queued songs.
• "Add folder to queue" adds each CUE/ISO track once.

Windows

• Always the latest version: the installer downloads the latest release each time (checked against its
  checksums), unless you choose an mq_ui file of your own. Without internet it offers the version built into the app.
• Windows is unsupported, but working as intended: confirmed several times by users, installs and SD updates included.

Installing and updating

• Already on diskOS Disco! 1.4.1 or newer? Update from the SD card: download mq_ui, sign it with your own
  keys and copy the diskos-update folder to the card (how). Your settings, music and stats stay.
• New install? Start from FiiO's stock V2.57 firmware (recommended). Installing over upstream diskOS or
  another diskOS build is not supported and can be buggy; restore stock first. See Install.

After updating

• Settings > System > About shows 2.5.7.
• The new version starts as a trial: play some music or tap Keep to keep it. If it doesn't start properly,
  the Disc goes back to the previous version by itself, or choose Go back.
• Something odd? Hold Volume Up from power-on to start FiiO's own interface once, and restart to come back.