METS: Metadata.csv accepts file and directory metadata

Remove distinction between file and directory metadata in the metadata.csv.
First column can be named anything, and a metadata.csv can have file and
directory level metadata.
METS: Handle metadata.csv with different columns

Store parsed metadata in a different OrderedDict for each file, so that not
all metadata.csvs have to have the same columns. Also, fix createMETS to
use return values and fewer globals.

WIP