Adds an automated test suite that runs JS tests using Tape. The tests are
run in Firefox using the remote code execution capabilities of Marionette.
Marionette's only well-maintained client is in Python, so we also have to add
Python dependencies, including a Pipfile.
bin/run_tests.py contains most of the plumbing for getting the test JS running,
including bundling it with Webpack, launching Firefox, and formatting the
output.
Michael Kelly