The old approach used a fast path for a very narrow set of
conditions and then used a slow path for everything else.
This approach required two sets of code,

- GenericCompositePolydataMapper2
- CompositePolyDataMapper2

and had performance issues as the slow path was slower
than OpenGL1 for some cases. This reworking consolidates
the two approach together. The basic approach is that
all blocks with the same VBO structure get grouped together
and rendered as one. The number of different VBO structures is
small so this results in a a small number of things to render.

Each of those things (handled with a Helper class) gets rendered
using its own VBO and IBOs with special code to handle the cases
where uniforms have to be changed between blocks etc.

The results are generally much faster. Some additional
optimizations have resulted in further performance improvements.
Generally this new class is as fast as the old fast path and
tens to hundreds of times faster for the slo...