Release packaging handling

[zazi]

Add a property to relate release packagings to mo:MusicalManifestation instances. Currently, MBZ differentiate between 5 (6) release packaging types which are:

musicbrainz_db=# SELECT * FROM musicbrainz.release_packaging;
 id |      name       
----+-----------------
  1 | Jewel Case
  2 | Slim Jewel Case
  3 | Digipak
  4 | Paper Sleeve
  5 | Other
  6 | Keep Case
(6 rows)

This probably requires the creation of a new class for release packagings, e.g., mo:ReleasePackaging. See also [1].

[1] http://wiki.musicbrainz.org/Next_Generation_Schema/Release_Packaging