Show validation errors outside details fields in G2 config

The problem is actually not with Drupal Form API errors, but with browser validation: the WOTD nid is marked as required, but when submitting the form with the empty WOTD (which is handled correctly by the WOTD logic), the browser blocks the form but does not open the wrapping details element.

The solution is therefore to either force the details open when a browser error happens, which means some JS ; or to remove the "required" flag on the WOTD node, since we handle an empty nid correctly anyway. Hence choose the latter.

Suggested patch. Also add some shortcut paths in the WOTD generation for the empty case.

Merged to current dev HEAD.

Automatically closed - issue fixed for 2 weeks with no activity.