Add support for encoding physical media format type

For an instance, we need another field for capturing physical media format type that is non-hierarchical under the container 1 type.

The field should ideally draw on a controlled list of standardized media formats, like this one:
http://metadataregistry.org/concept/list/page/3/vocabulary_id/145.html (ha! It is a long list. Next version will be cleaned up, shortened, and published in spring 2015.)