Significantly better performance with EdgeVisibilityOn

The old code was rebuilding the shader, VBO and IBOs twice per frame
when edge visibility was on. Bad. The new code keeps a seperate IBO
for edges making it much faster (100 times) at the cost of another
IBO.

Change-Id: I479c1c2940501bb144e1f92b99c11a07b274a9aa
Merge topic 'faster_edges' into master

6b8ef814 Significantly better performance with EdgeVisibilityOn