Replace user "status" with "availability"
- Currently, user status is derived by looking at events they created. Instead, look at non-cancelled invites they are attending.
- Prepare for on-user caching.
- Mostly remove "Sporradic" as a status, although I left room for adding more information later.
- Called user.query.
- Viewed profile.
- Viewed hovercard.
- Used mentions.
- Saw status immediately update when attending/leaving/cancelling a current event.
- Created an event ending at 6 PM and an event from 6:10PM - 7PM, saw "Away until 7PM".
Reviewers: chad, btrahan
Reviewed By: btrahan
Differential Revision: https://secure.phabricator.com/D12833