Remove now-unused 'startTime', 'endTime', and 'location' properties for items
Remove unused 'datesEqual', 'dateLessThan' and 'dateGreaterThan' functions
Remove date view for now, leaving just showing items grouped by tag
Work toward adding new items with associated tag
Remove old GroupableMixin
Start switching to use item_tags join model
Hacky way to get the items to display again
Make relationships not-async
Slight formatting fix