Move the field_hide_from_search configuration to the omnipedia_search module if possible

Some research will be needed to determine how complicated getting this to work correctly will be. Drupal core presumably supports this.

Our Node class currently has a WIKI_NODE_HIDDEN_FROM_SEARCH_FIELD class constant and isHiddenFromSearch() method which will likely need to be removed unless some really clever solution is found to have the omnipedia_search module add them dynamically or via some hook.

This is currently blocked by #4 (closed).