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 :)
can you make sure this is right? I have a feeling that `params[:id]` refers to the attendance id, not the tea_time id. Pretty sure tea_time id in this situation should be `params[:tea_time_id]`.