Selenium (part 1)

First of several happy-path Selenium tests for [ORA-659](https://openedx.atlassian.net/browse/ORA-659).
This tests the self-only flow -- I plan to add more tests in the next few days, using this as a starting point.

@stephensanchez @jzoldak Please review.
Should it be ```self.q(css=".action--submit").first.click()```?