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!

lib/util.php

@@ -2004,7 +2004,11 @@ function common_user_property($property)
         return $profile->$property;
         break;
     case 'avatar':
-        return $profile->getAvatar(AVATAR_STREAM_SIZE);
+        try {
+            return $profile->getAvatar(AVATAR_STREAM_SIZE);
+        } catch (Exception $e) {
+            return null;
+        }
         break;
     case 'bestname':
         return $profile->getBestName();