Added MP4Tags (m4a, mp4, alac) support
Fixed ID3 date tag support
Tagger: fixed_tags (from arg): added support for multiple values per tag (using list)
Merge branches 'tagger/mp4_support' and 'tagger/tag_arg_multiple_values_per_tag'

* tagger/mp4_support:
  Fixed ID3 date tag support
  Added MP4Tags (m4a, mp4, alac) support

* tagger/tag_arg_multiple_values_per_tag:
  Tagger: fixed_tags (from arg): added support for multiple values per tag (using list)