Add E2E tests (to the CI)

They're definitely working locally using Selenium & things, but getting it to run on the CI will be a bit of a pain since I'm halfway across the world from the network/machines. Steps:

Clone beat.tutorial.prefix and use the prefix folder for the tests
Figure out how to run the beat.editor REST server in the testing environment
Figure out how to expose the geckodriver executable (different for Mac & Linux!) and add it to the $PATH

Edited Aug 13, 2018 by Jaden DIEFENBAUGH