Added new shader hint for modifying geometry

Added new shader hint for modifying geometry

Culling can only be performed when the vertex shader doesn't move
vertices outside the bounding box. Custom shaders can specify whether
they dont change geometry by setting the hint DOESNT_MODIFY_GEOMETRY.
This will turn culling on for the actors that this shader is used
to render.

Further clean up applied.

Change-Id: Ia28ba7bc0f23613316c9b21a536a94e851337bd2
Signed-off-by: David Steele <david.steele@partner.samsung.com>