Add a defcustom for shadowing the `window-configuration-change-hook`

My `window-configuration-change-hook` has a few functions that apparently
run pretty slowly, especially when called once for each window I have
open - easily up to six or seven times. This customization option allows
the user to decide whether they'd like to shadow the hook with nil while
switch-window is running, and avoid the unnecessary calls to the
-change-hook, especially since the temporary changes to the window
layout that `switch-window` does are hopefully not pertinent to the
functions in `window-configuration-change-hook`.