Update metadata parser

[bcomnes]

Use music-metadata everywhere. It does a much better job than the old version we were using.

Also a few other things:

• Delete dead code
• Use bufferlist instead of a copy-pasta from2

Closes #185

[bcomnes]

This improves the metadata and compatibility to a whole lot more files, even ones missing tag frames all together, and is generally a faster scan!

The drawback is that some of my larger DJ set type songs hang this up for some reason, and can cause 30-40 second delays on some tracks (specifically ones that were recorded from Shoutcast streams back in the day... don't ask).

Going to merge this now, since it provides some critical metadata fields like duration of all files... but we should figure out whats going on with these files and maybe try to send an upstream fix.