Made selenium testing work with the docker dev.

Went back to making the amara-dev Dockerfile based off of our regular
dockerfile.  I'm not sure what I was thinking, but that other way
wasn't working

Added script to build images manually.

Set the hostname for management commands/test commands to
unisubs.example.com.

Make test.py run the tests under xvfb-run, so that the selenium tests
can work.

Added a bunch of stuff to the amara-dev Dockerfile so selenium works.
Couple of fixes to make selenium slightly closer to working
Couple more changes to make the selenium tests work
Merge branch 'docker-tests' into staging