Added "KKB Page" panel page variant for node/%node.

This module holds a `node/%node` panel page variant called "KKB Page".

"KKB Page" is a clone of the `ding_page` modules "Page" panel page
variant.

"KKB Page" has one minor change compared to "Page". The "Opening hours
by week" content pane from the `opening_hours` module has been added
to the top of the left sidebar.

The module also enables Opening Hours for the `page` node type.