Attendance update route can now take a reason from params. Updates #78

Also not tested. All I could do in a few minutes before going to work. 

- Created a new Attendance controller and pointed update route to it
- Passed in `reason` param to `flake!` method as part of opts and assigned it
to the record. 

This could use a unit test for `flake` and a feature spec as well. I'll see if I can
do it tonight :)
Positive it's right. The `update_attendance` route is subordinate to the `TeaTime` resource, to `:id` gets bound to the first ID param in the URL, which is the TT's.