base

Add display manager skeleton.

The purpose of this change is to remove direct reliance on
SurfaceFlinger for describing the size and characteristics of
displays.

This patch also starts to make a distinction between logical displays
and physical display devices.  Currently, the window manager owns
the concept of a logical display whereas the new display
manager owns the concept of a physical display device.

Change-Id: I7e0761f83f033be6c06fd1041280c21500bcabc0