Implemented an extended user profile based on a patch from Jethro Carr (issue 510).

Changes with respect to the original patch:
- use Gconf instead of separate table / data scheme
- better form validation for URLs and emails
- no htmlentity-encoded contents in the database (pluf automatically safe-encodes
  stuff before it writes out contents into templates)
- add visual separators in the form views to have a distinct view of basic
  (important) data and other data which are only displayed in the public profile
- give a hint about the maximum display size of 60x60 px^2 and use max-width and
  max-height in the templates to avoid nasty distortions by the browser
- use target=_blank and rel=nofollow on the twitter and website links in the profile
- some whitespace / formatting / code style fixes

www/media/idf/css/style.css

@@ -104,6 +104,11 @@ table.form th {
   font-weight: normal;
 }
 
+table.form td.separator {
+  font-weight: bold;
+  text-align: center;
+}
+
 .px-message-error {
   padding-left: 37px;
   background: url("../img/dialog-error.png");