Implement duplicate item validation at the model layer
Duplicate item validation implemented at view layer
Added new form for adding to existing lists, implemented duplicate item validation into it
Changed home page view from a function to a generic class based view
CBGVs working without ViewAndAddToList as a CBGV.
Finally fixed the viewing/adding list items in views.py with a CBGV. TIP: NAMED GROUP 'pk' IN urls.py