Don't display drag info or cog

Displaying drag info is slow. Displaying the center of gravity is okay, but looks a bit weird.
Allow panning around with the root window

You can now drag the root window around to pan around the desktop.

Dragging the world on a given physical display will select all clients
on that display for moving. When the drag is complete, the clients
will move to their new physical displays and virtual desktops.