WIP Selenium testing

couple changes:
1) made public facing default landing page (index.html) extend base-admin.html, which includes base.html. important because:

2) added dummy DIV "bottomAnchor" on the base.html page that selenium can look for to make sure the page is fully loaded

3) added some very WIP first pass selenium tests which run Firefox and click on things.  My goal is to have the attendee prereg form be covered pretty well with some selenium testing as a first start for getting some functional testing up.
Whenever anyone does anything with Selenium, the very first thing they have to do is write some variant of a ``wait_for`` method.  Why does Selenium not include such functionality?  I have no idea!

I'm ambivalent about using Selenium for testing Uber at all.  We can get most of the way there with Python unit tests, and the extra effort to write Selenium tests is very high relative to the value it provides.  And the prereg process is simple enough that I don't expect there to be any serious issues with differences between browsers.

With that being said, selenium tests are nice to have.  So while the effort might be better spent elsewhere, I'd be happy if we ALSO had selenium tests in addition to our other tests.