Changes in this commit:
* Changed file organization (regarding configuration, added everything that
  has to do with configuration to phplib/config-template.php). You can now add
  URL to this config file (instead of changing it everywhere).
* Added a very simple index file that links to the registration page & the
  login page.
* Login attempts are now blocked if someone submits more than 5 login attempts.
  Potential weakness in the current approach is that malicious users could
  just remove the session cookie and reset the counter to 0, it would probably
  be better to store something in the database (IP and login count).