First commit at generic adding items to collection
Updated JS to be generic on collection items
Added add/remove item endpoints

Generic API endpoints used for adding Events or EventGroups to a user
collection
Basic EventGroupSerializer
lint
Added remove_item on Collection model

Fixed a bug on add_item to make it generic also
Correct JS hooks in the html
Added case statements to handle Event/EventGroup
Serialize Event and EventGroup with class_name

Used in the JS to distinguish items
Remove item and return full item
Render out EventGroups which have no `type`
Added JS template for groups
Updated serializers to use get_absolute_url
Return 404 if no item is found
Assert we don't get both an event and group
Merge pull request #45 from ox-it/groups-in-lists

Groups in lists