New settings for private installations

- The site name in the titles and "about" page can be changed from
  dpaste.de
- The Gist feature can be disabled (both the UI and the code that does
  the POST)
- A different URL can be given for jquery(.min).js besides google, such
  as beside the local static files
Merge pull request #66 from welshjf/site_settings

New settings for private installations