Make responses editable by admins - Backend

[avishkar58]

Create a new AnswerAdminAPI which has a PUT method that does the following:

• Accept event_id, answer_id and value parameters
• Ensure the logged in user is an admin for the given event
• Update the answer with the given ID to the given value
• Log somewhere (eg an AnswerAudit table) the original value of the answer and the update made to it, with the timestamp and user_id of the update.?

TODO: Should this just create a new response and leverage the existing audit mechanism?

[bdhobare]

It would be consistent and nicer to have it follow the existing audit mechanism (relying on is_active columns). When doing an actual audit, the queries would be consistent and follow the same pattern (filtering by is_active).