Keep MPD's footprint small until playback is requested.

A Java object to send logs on the android side.

Eliminate yet another access to the global ConfigData instance.

Let MainOrThrow() forward it to mpd_main().

Deinitialize the logging library after the last exception handler,
because that one could still need it.

Use `AtScopeExit()` to ensure it's always called, even if an exception
was thrown.