Add Optimistic Locking in Future

http://railscasts.com/episodes/59-optimistic-locking-revised?view=asciicast

Prevents updates to the same entry simultaneously from two sessions from screwing up stuff

Not necessary at this point in time because our admin side usage is low.

KIV for future addition.

Read the linked Railscasts episode first to understand the intended optimistic-locking behavior. The issue names no files, tests, or entry points, and explicitly defers the work because admin usage is currently low. Done criteria and implementation scope would need to be established before starting.

Written by the indexing model from the issue text.