This integrates hair collisions with the new cloth collision system, greatly improving reliability, and reducing the amount of hair-specific code paths in the cloth code. The removes all the point constraint based collision stuff, instead implementing segment impulse based collisions, using the same collision response code as the normal cloth solver. The hair system can now also collide with the emitter if it is a collision object. Reviewed By: mano-wii, Sebastian Parborg Differential Revision: https://developer.blender.org/D6545