Recent authors

Added an endpoint that allows you to check whether an OAE user has made
a change to a pad in the last 15 minutes. Edits are tracked per pad/user
and are periodically cleaned.
Added a REST endpoint to manually mark a user as a recent author for a pad
Send “publish” events to RabbitMQ for OAE to pick up
PR follow-up

Binding to oaeproject/amqp#0.1.8
Re-introduced TTL in recentauthors
Cleared up attribute pool
Merge branch 'recent-authors' of https://github.com/oaeproject/ep_oae into recent-authors
Follow-up on recent authors functionality
Use the new `userLeave` hook and fix bug in RecentAuthors
WIP implementing new etherpad designs