Add Layout Meta Editing

[kittsville]

There's currently no way, within the UI, of editing a layout's name, slug or short description. An edit key style pop-up would be the easiest way of adding this functionality.

This will probably involve adding a new JS object to specifically handle pop-up behaviour, as to keep the JS DRY.

There's also some styles which should be pulled out of the edit key pop-up and added to the pop-up class instead.