Adds methods and tests for Datastream::UOIS, #is_series?, #is_program?, #is_video?, #is_video_clip?, #is_image?, #is_transcript?, #is_collection? (and stubs for #is_audio?).

Closes #88. Closes #86. Closes #85. Closes 84. Closes #83. Closes #82.
Rearranges artesia ingest fixtures. Again. Files named according to content, in spec/fixtures/teams_asset_files/.