Put sheriff data into a participant field

[andymeneely]

• Remove has_many association from Reviewer and Participant
• Get on_optimize to work
• In rake run:analyze populate a new field on participant called sheriff_hours that totals the number of hours that that participant was on rotation prior to the creation of this code review. Aggregate all types of sheriffs into this count - no need to filter out different types of sheriffs
• Also in rake run:analyze aggregate the above count into the code review so we know how many hours the code review had in total.
• Add a release_filepath metric that averages the total number of code review hours per code review.
• Make the association in rake run:results that tests this

Do this in ActiveRecord, not straight SQL.

[kaylaerdmann]

I removed uniqueness from the optimize dev_id in the sheriff model, as a sheriff can show up for multiple rotations.

[andymeneely]

Makes sense. That's fine.