Make formats more configurable

[Aquassaut]

Ideally that entails:

• Have a user conofigurable list of formats
• Make that list have directives like "transcode_to", "ffmpeg_extra_flags" and such.

This would allow people to put up their own requirements as far as what to do with their audio files. One example is someone who listen to a show that he has in FLAC on a device that doesn't support FLAC. That person should have a way to tell this application that he always wants FLAC to be transcoded into mp3.