Cycles Hair: Addition of render settings and static BVH strand width scaling

Addition of a RNA function to toggle between the hair settings and rebuild the cache. This enables the usage of the render step, child number and full display percentage with f12 rendering.

A scaling to the strand radius has also been added for the static bvh. This only matches up with dynamic for uniform scaling.

A very small fix is included for multiple uvs/vertex colours when using child particles.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54186 954f8c5b-7b00-dc11-b283-0030488c597c