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

src/IDF/relations.php

@@ -43,6 +43,8 @@ $m['IDF_Conf'] = array('relate_to' => array('IDF_Project'));
 $m['IDF_Commit'] = array('relate_to' => array('IDF_Project', 'Pluf_User'));
 $m['IDF_Scm_Cache_Git'] = array('relate_to' => array('IDF_Project'));
 
+$m['IDF_UserData'] = array('relate_to' => array('Pluf_User'));
+
 Pluf_Signal::connect('Pluf_Template_Compiler::construct_template_tags_modifiers',
                      array('IDF_Middleware', 'updateTemplateTagsModifiers'));