Notice on p2p landing page (affects VBO on admin UI pages)

This affects VBO on any admin UI pages. The VBO select all checkbox element array does not have a `#parents` key and springboard_base_form_element() was previously assuming every element has it.

This PR adds a check for that key before adding the CSS class that uses it.

I also split up the class array so that the order of classes is preserved, although I don't think that matters much.