Changes following the UX review

This is not yet complete, but I'd like to get some feedback. Things still left to do:

 - [ ] Create a page explaining the DDD process (submission, voting, etc...) and link to it from a "New to DDD?" link on the home page.
 - [ ] Require the user to enter a name and email address (or capture them) when logging in with OAuth as a primary login.
 - [ ] Prompt for confirmation (jquery dialog) when deleting a session.
 - [ ] Change the styling of the speakers page to add some visual separation between speakers.