Drop file crc from music database

Pretty straight forward.  We basically only used the CRC stuff when looking up a filename in the database, and the strFileName column is already indexed, so using the CRC of the filename was actually slower, as the column wasn't indexed.

The last commit drops the unused columns (CRC, and some old thumb stuff) from the song/album/karaokedata tables.  This isn't strictly required, so am happy to drop if it's thought that this cleanup isn't required.  The 'cleanup' in this case leads to quite a bit of code (54 lines), so I'd almost prefer to leave these unnecessary columns floating around, as we've tended to do in the past.

Includes a database update.