Properly unlink all old avatars when deleting/uploading a new

We're also now using $config['image']['jpegquality'] to determine the
quality setting for resized images.

To set Avatar max size, adjust $config['avatar']['maxsize']

The getAvatar call now throws exceptions too. Related changes applied.
Now let's move Profile->avatarUrl to the Avatar class!

plugins/QnA/actions/qnashowanswer.php

@@ -96,7 +96,11 @@ class QnashowanswerAction extends ShownoticeAction
             throw new ServerException(_m('User without a profile.'));
         }
 
-        $this->avatar = $this->profile->getAvatar(AVATAR_PROFILE_SIZE);
+        try {
+            $this->avatar = $this->profile->getAvatar(AVATAR_PROFILE_SIZE);
+        } catch (Exception $e) {
+            $this->avatar = null;
+        }
 
         return true;
     }