Improved webinterface and web-based registration

Today, two items on the todo list for this server got done:

• The web page at http://jabber.rueckgr.at/ got a much nicer web interface. Until now, the web page was just a static HTML page in the style of the 1990s. From now on, Drupal is used.
• Users may now register new accounts using a web interface. Of course, in-band registration using your favourite XMPP client still works.