Use Unicorn with Heroku

Setup unicorn and enabled rack-timeout so that if the unicorn workers
get killed because of a possible time out then rack-timeout should
throw an error that appears in the logs (which doesn’t happen if the
unicorn worker is killed)
Merge branch 'master' of https://github.com/ministryofjustice/scs_appraisals

Conflicts:
	Gemfile.lock