implemented createuser within the normal UI

Fixes #110:
* Implemented createuser within the normal responder.php/BMInterface.php UI (BMInterface.php is correct, rather than api_core.php, because we're not actually setting session variables for the user's browser, we're just making database objects, so it's not a special case like login/logout)
* Cleaned up the main landing page so / redirects to /ui/ now
* Stopped installing users by hand

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