Extended M-to-N edit-ability to everything

1. Moved most Controller Actions to Base Controller
2. Added Controller Actions for Adding and Removing M-to-N relationships
3. Added BaseModels file with improved base Model classes
4. Split Models into multiple files, and added Metadata to each Model
5. Unified formatting of Create and Edit Views
6. Extracted related-item-lists to _Related View
7. Moved Delete, Details, and Index to shared, as they were no longer
unique
8. Replaced individual _SomethingActions with single shared _Actions
9. _Actions also replaces _RemoveAssignment