Removed deprecated model Entity. Also started on migration and transformation stuff.
Started on migration stuff.
Improved the AMU finder for agents in MODS (especially regarding namespaces), and fixed some tests.
Merge branch 'master' of https://github.com/Det-Kongelige-Bibliotek/valhal

Conflicts:
	app/models/entity.rb
Removed Entity model (deprecated since we chose to reuse the name 'Work' instead).