Wrap palette references with a PaletteRef object.
Add a cache of PaletteReferences to WorldRenderer.

I don't expect any perf improvements by using this
cache, as you're simply moving the row lookup from
render-time to fetch-time. However, this is a
cleaner abstraction, and allows us to fail early
if the palette doesn't exist.
Move effects to WorldRenderer palette lookup.
Pass a PaletteReference to RenderPreview.
Pass WorldRenderer to IRenderModifiers and replace more palette lookups.
Extract auto-selection-size into its own interface.
Let parachute cargo render themselves.

This allows for tanks and other multi-sprite
actors to render correctly while dropping.
Pass WorldRenderer to Render().
Remove RepairIndicator dependence on target RenderSimple.

This also fixes the case where the building palette doesn't
match the indicator, and saves 2 trait lookups per tick.
Ditto for RallyPoint.
Ditto for GpsDot.
Ditto for Corpse.
Make RenderSimple.Palette protected.
Store normal vectors in the palette texture.
Implement vxl parser.
Implement hva parser.
Add renderer support for matrix uniforms.
Add a Vertex ctor with z-pos.
Add renderer support for toggling the depth buffer.
Add voxel renderer.

Only supports the Gl renderer (needs Cg shaders).