The goal is to convert the legacy hair system to the new curves object at run-time for drawing. This should allow us to get rid of all drawing code that was specific to hair particle systems. Then we can focus on improving the rendering of the curves object without too much code duplication.
Todo:
* Move conversion code to a different file that can be used from the operator and modifier.
* Propagate attributes in modifier from surface to curves:
* UVs.
* Vertex Colors.
* Support hair length/intercept attribute for curves in cycles.
* Support close-tips for curves in cycles.