Non-trivial re-tooling of libraries, models, and tests:
1. Changes namespace from Artesia::Ingester to Openvault::Ingester::Artesia
2. Moves saving functionality out of Openvault::Ingester::Artesia into ArtesiaIngest#save_all!
3. Adds convenience methods Datastream::TeamsAssetFile#set_xml and Datastream::UOIS#set_xml for setting xml via Nokogiri::XML.parse. These are compliments of #to_xml inherited from ActiveFedora::OmDatastream#to_xml.

Closes #66.