Page Shot v5 on Stage for testing

We’ve gotten Page Shot v5 on stage, and the stage version can be installed from this page: https://pageshot.stage.mozaws.net/homepage/install-test-local.html

There’s not a lot new in this release except for some A/B tests. For Stage we’ve increased the probability of getting assigned to an A/B test, so you have 25% chance of getting one of the 3 tests (and a 25% chance of being in control for all of them). Stage data will be going into Google Analytics, and give us some sense of whether we’re able to usefully analyze the A/B testing results.