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/templates/idf/user/public.html

@@ -2,9 +2,39 @@
 {block body}
 <table class="form" summary="">
 <tr>
-<th></th>
+<th style="text-align: right">{if $user_data.avatar != ''}
+    <img style="max-height: 60px; max-width: 60px;" src="{media}/upload/avatars/{$user_data.avatar}" alt=" " />
+{else}
+    <img src="http://www.gravatar.com/avatar/{$member.email|md5}.jpg?s=60&amp;d={media}/idf/img/spacer.gif" alt=" " />
+{/if}
+</th>
 <td>{$member}</td>
 </tr>
+{if $user_data.description != ''}
+<tr>
+<th>{trans 'Description:'}</th>
+<td>{$user_data.description}</td>
+</tr>
+{/if}
+{if $user_data.twitter != ''}
+<tr>
+<th>{trans 'Twitter:'}</th>
+<td><a rel="nofollow" target="_blank" href='http://twitter.com/{$user_data.twitter}'>{$user_data.twitter}</a></td>
+</tr>
+{/if}
+{if $user_data.public_email != ''}
+<tr>
+<th>{trans 'Public Email:'}</th>
+<td><a href='mailto:{$user_data.public_email}'>{$user_data.public_email}</a></td>
+</tr>
+{/if}
+{if $user_data.website != ''}
+<tr>
+<th>{trans 'Website:'}</th>
+<td><a rel="nofollow" target="_blank" href='{$user_data.website}'>{$user_data.website}</a></td>
+</tr>
+{/if}
+
 <tr>
 <th>{trans 'Last time seen:'}</th>
 <td>{$member.last_login|dateago}</td>