Add basic support for VorbisComment DATE tags

Since Android doesn't support DATE tag itself, just use it to extract
the year from the ISO date (if the YEAR tag isn't present) and fill
media database with it.

Require: http://review.cyanogenmod.org/#/c/104193/

Change-Id: I30f86bb05cc8ab158ca538f899a124a4bf8eb9f0