Reorganization into multiple repositories

[wwahammy]

As mentioned at #50 by @mattsm, moving tests into a separate repo would help organizations where they have unique or proprietary tests. (We, of course, encourage all organizations to upstream all tests they possibly can) Doing so would simplify those organizations updating boardfarm from upstream or submitting their improvements to boardfarm.

Are there other examples of files which should be moved out? I don't think we should move out the boardfarm_config_example.json but I know I just keep it there even though that's a bad practice.

Additionally, how should we reorganize the repos so that it's straightforward to get started? I'd like to have a simple way to download the main and tests repos in one command. Additionally, running an update command should give you the latest copy of the tests (or your version of the tests). Perhaps a script in a third repo?