Adding move window functionality for free form desktop

This patch adds the capability to move / drag a floating window on
the desktop when it has a non client decor capition.

It also adds the framework necessary adjustments to keep the window
in a visible area without relayout'ing the window upon move.

Bug: 21738328
Bug: 23176762
Change-Id: I0927e98902d8172f58d21c19c249936a81181678