OpenGL: use the "glm" library for GLES2

Replaces the GLES1 built-in matrix operations (incomplete, just
infrastructure).
OpenGL/Canvas: move code to VertexPointer.hpp
OpenGL/Texture: use class ScopeVertexPointer
OpenGL/Texture: GLES 2.0 implementation

New shader for textures.  Untested, but compiles.
OpenGL/SubCanvas: GLES2 projection using the "glm" library