This implements collisions in the solver of the cloth brush/filter. It
uses the scene colliders as a regular physics simulation.
There are still some parameters (friction, distance to the surface...)
that can be exposed as properties in later patches.
To make it work it needs an object with a collider and a softbody
enabled. The softbody is needed because otherwise collisions relations
are not created and the solver can't get the colliders. I'm not sure if
there is currently a way to request the collisions relations from a
Thanks to @Sebastian Parborg (zeddb) for helping me with the implementation.