Adds notifications model, and migrations. Adds associations to other models.
Keeping this branch updated with master while I'm still working on it.
Merge branch 'master' into notifications
keeping up to date until notifications functionality is finished
Merge branch 'master' into notifications
Forgot to add type to some add_columns
Fixes a few typos and other issues with notifications
Notifications are finished
Finishes notifications, merges them into main app