Add a new-look root page

Removes the "normal" UI in favour of a simplified header, and large text
describing the purpose of the ETM. The call-to-action buttons are much
larger, and centrally placed on the screen so as to be hard to miss.

Still to be done:

  * NL translations
  * Cross-browser testing
  * "Select a preset" page
  * Sponsor logos (currenly omitted due to some sponsor logos not
    having transparent backgrounds.