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 'bar-chart-colors' into pv-master

b2e4fb38 Added colored bar charts, along with a test
Merge remote-tracking branch 'pvvtk/pv-master' into HEAD

* pvvtk/pv-master:

Change-Id: Ib2f59ff5809fa6d9e7ebc75d57fa40fb72fa9e9f
Merge topic 'glsl_instancing' into master

4b18a9b5 Had to rebase as master had comflicts
4dea04ea Add support for OpenGL32 instancing in GlyphMapper
fix opengl es issues with glyphing code

ifdef out the instanced rendering when on opengl es 2.0

Change-Id: I44008775f425ab5f5d5fab39d42550b28513c148
Expand support for the OpenGL2 backend

This change makes more modules dynamically switch between the
rendering backends if they have no OpenGL code, or introduces some
ifdefs in the case of RenderingParallel (which may not be functional
at this stage). Added RenderingFreeTypeOpenGL2 which will also need
some additional work before it is properly integrated with the new
rendering backend, but it surprisingly seems to render on the
desktop.

This commit contains everything needed to get a minimal ParaView
build using the new rendering backend for polygonal rendering.

Change-Id: If8676d41d263b046a54060965fc760b5d4bd64a1
tk: update to support 8.6

Change-Id: Ic35789eb6f3b05771bb1cbd3c24adf9ea0e2252a
Merge topic 'glyph_ios' into master

4e9baa2d fix opengl es issues with glyphing code
Merge topic 'support-tcl-8.6' into master

9f4afe40 tk: update to support 8.6
Merge topic 'opengl2-backend' into master

666ade8a Expand support for the OpenGL2 backend