Add support for OpenGL32 instancing in GlyphMapper

Currently disabled as no 3.2 contexts are requested, but this patch
adds support on an OpenGL 3.2 context to use instancing for rendering
glyphs. This required adding some additional capabilities to the VAOs
so that they can handle matrices and divisors. This patch shows slightly
better performance on a 2.1 context and about a 100% improvement on
a 3.2 context. Picking on the 3.2 context path still needs some minor
work.

Change-Id: Ifb59184e9e3184b664fb642c5ffa73f4f268dd51
Had to rebase as master had comflicts

No new functionality etc,  Simply merging due to rebase.

Change-Id: I5b2417548cbce35acf9121baf6470f1c38d5a1fb
Merge topic 'glsl_instancing' into master

4b18a9b5 Had to rebase as master had comflicts
4dea04ea Add support for OpenGL32 instancing in GlyphMapper