teams checkpoint

quick and dirty - implement all teams backend functionality, with
minimal frontend.

i spent a while looking into angular, but when i realized we'd have
to escaped_fragment, pre-rendered html for SEO, i decided server-side
rendering would keep the codebase simpler for newcomers.

so, basically i bailed cause i'm a coward

anyway, this doesn't talk to the pledge app yet and a bunch of stuff
is missing, but this supports:
 * login/logout
 * dashboard for logged in users
 * ability to make a new team page
 * ability to edit an existing team page
 * team page urls are based on (editable) team page titles and updated
   when they change, and old urls continue to work

missing:
 * integration with pledge service
 * uploadable images
 * any kind of looking nice
 * markdown support for description field
 * video types other than youtube

misc todo:
 * clean up form validation