Adds an animation to the grid plugin. The animation takes the current window,

renders it to the growing grid box and slowly fades out into the default
orange glow box.

Also adds 2 options ccsm for the grid, one to turn this animation off, and
another to change the grid animation duration.

This also changes the default grid duration from 250 ms, to 350ms.

(LP: #689792). Fixes: https://bugs.launchpad.net/bugs/689792.

Approved by Daniel van Vugt, PS Jenkins bot, Brandon Schaefer, MC Return.