First step toward VectorStorm 2.0 -- Renderer_OpenGL2.

No more support for fixed-function rendering, bloom shader is no longer
part of the base rendering system.
Now loads 'default' shaders from data.

(Need to work out the right way to make those default shaders)
Setting texture samplers in shaders.
Removing double - on vsTransform2D matrix conversion
Working toward new explicit matrix support for shaders.

Works for 2D rendering, next step is 3D rendering.
Explicit matrices now work for both 2D and 3D.

Couple minor issues remain to be sorted out, and a whole bunch of code
cleanup.
Merge branch 'v2_matrices' into v2
Removes some old API calls.
Fixes worldToView matrix for 2D scenes with cameras not at origin.

(or cameras with non-zero rotations)
Removes last vestiges of fixed-function pipeline matrix handling
Support for #version statements in shaders.
Changes the expected filename of the default shaders.

"default.vs" -> "default_v.glsl"
"default.fs" -> "default_f.glsl"

(Need to figure out the proper way to handle these, still)
Little improvements to OpenGL capabilities testing.

Still needs a lot of work in terms of coping with insufficient OpenGL
support.
Converts vsScreen to a singleton.

Finally got tired of vsSystem::GetScreen().
Initial implementation of rendering using a pipeline.

(Current default pipeline mimics behaviour of old vsScreen::Draw() function)
Adds configurable rendering pipeline
Fixes sign-compare warning
Fixes render of debug scene.

(Need to debug why the debug scene needs to be drawn in a separate call
to RenderDisplayList.  Not sure why it can't be loaded onto the end of
the main one)
"Blit" as a render pipeline stage.

Still arguing with myself over whether an explicit "blit from scene to
window" should be required in a pipeline.  Or whether, in fact, the
whole hardcoded 'scene' and 'window' even make sense, and the 'scene'
should be pulled out of the renderer entirely.
Removed the 'DefaultShaders' source file, added as data files.

Note that there's currently no CMake build setup to automatically copy
VectorStorm shaders (or other data files) into a game's data.  There
probably never will be.  Instead, these data files are provided for use
by games which don't want to implement their own default shaders.

Regardless, any VectorStorm game will require a default_f and default_v
shader, for use when rendering anything which doesn't explicitly
reference a custom shader in its material.