This fixes the bug where many bindings don't work if numberlock is set.

This new feature creates a 'selected windows' buffer which allows
the user to select windows. These windows are then automatically
made the argument for a Wml window operation such as shifting.

This is great for when one wants to apply an action to a set of windows
which are too difficult to describe with Wml expressions.

In addition, I have added a bunch of mouse bindings and key bindings
to this.

 - Added ShiftAndSwap functionality, which allows user to shift a
   <windowset> to a <workspace> and then swap that workspace with
   another <workspace>

   e.g. move Spotify to workspace 's' and put workspace 's' on the last
   monitor.

   This replaces the shift-and-follow as this is more powerful (shift
   and follow just puts the "shifted-to" workspace on the current
   monitor.)

   ofc if the two workspaces to swap are not visible, this just operates
   as a normal shift command.

 - Moved more dragging functionality to the Dragging.hs file and cleaned
   it up a little. More is certainly needed.

 - With the more powerful dragging functionality, many bindings are made
   redundant. I replaced one of these redundant bindings (button13 ->
   mouseWheel). This used to move the focused window around the stack,
   but this has been made redundant by the drag-to-swap functionality
   (button14 -> left-click-drag), so now it changes the master region
   size.

Dragging a window will leave a hole behind until it reaches its final
destination, making it look a little better.

Now I've also implemented drag so that when ending the drag with a
right-click it tiles the window on the screen it's currently on.

It is still pretty jenky and very much a WIP.