Set up sbt build
Add README contents, add tags and verify scripts
Add UI
Add server skeleton
Add route for shutting down the system
Add route for static content
Add route for getting messages
Add route for posting messages
Add authentication
When getting messages, send completer to per-user Gabbler actor; send posted message to all Gabblers
Add simple long polling behavior to Gabbler
Change Gabbler's behavior from using mutable state to become-based state machine
Add timeout parameter
Add timeout to Gabbler life cycle
Replace become-based state machine with FSM-based one