UK: metadata serializer
UK: MetaDataObjectPermissions to use permissions on the xform object
UK: add MetaDataViewSet
UK: test add metadata via api
code refactor: use self._add_meta_data
UK: set blank=True for MetaData fields that should allow null values
UK: code refacor: allow metadata with no file attached
UK: add post maplayer via the metadata/api
UK: code refactor
UK: add id field to MetaDataSerializer
UK: code refactor
UK: test delete metadata
UK: test csv upload with application/octet-stream
UK: test add media url
UK: allow urls that may end with a number e.g mp3, mp4
UK: use MetaDataFilter, filters by user's XForm permissions to access MetaData
UK: updated test to include authentication
UK: use xform permissions for metadata
UK: custom content negotiaition, media renderer and return file data if file extension is specified and we have a file
UK: add metadata as xform field