This replaces the cmake options WITH_NEW_OBJECT_TYPES and
WITH_NEW_SIMULATION_TYPE with two experimental userpref settings:
- use_new_particle_system: Enables the point cloud type and the simulation editor.
- use_new_hair_type: Only displays the add-operator in the add menu for now.
We could also create a cmake option for the new hair type, but I don't really see
a benefit in that.