move scratchpad: hide visible scratchpad container
move scratchpad: hide visible scratchpad container

This makes it so running `move [to] scratchpad` on a container already
in the scratchpad does not return an error. To match i3's behavior, a
visible scratchpad container will be hidden and a hidden scratchpad
container will be treated as a noop.

1ace/sway,ascent12/sway,1ace/sway,ascent12/sway,1ace/sway,SirCmpwn/sway,ascent12/sway