because rodio struggled to load some
(possibly broken, but still playable) audio files.
this is not perfect and sometimes suffers from
small lags, and it uses song_finished_polling
instead of being event-driven.
server can now source its database and files from
another server, but it will have its own
queue and appears as separate to clients.
the client now has gui-syncplayer-{local,network}
modes which show the gui and also play the songs.
using a syncplayer-network mode now automatically
enables the cache manager, which should make
waiting for songs to load less frequent.
