Clean up front page UI and video elements [OPEN-407]

The purpose of this change is to remove our stale, early-2012 marketing text from default Open edX instances. Cribbed some text from [the apache welcome page](http://wiki.jetbrains.net/i/images/3/31/Figure_3_apache_installed.png) and [the django welcome page](http://pystar.github.io/pystar/_images/itworks.png) - I'm open to suggestions here.