systemd service files

Resource limiting features of systemd will be very useful in the future :)
Now use salmon-mail from pypi

[ci skip]
Call python from the virtualenv directly

[ci skip]
Fix systemd unit files

systemd looks for a path and ignores ${} variables

[ci skip]
Use Celery's test runner
Pull in queue tests
New tests for queue and website
Merge branch 'master' into deploy