[UX] Add a "Place in a layout" action for menus in the menu listing page.

This is an idea that was mentioned in #1278 and could be part of the #1839 meta-issue...

So the idea is basically to have an additional "Place in layout" action available in the drop-button in the "Operations" column (mockup):

...this would pop up a dialog asking which layout to add the block to, and upon selecting a layout, would redirect to the "Manage blocks" page for the selected layout, perhaps with a "Select region" prompt?