brute force implementation of the surface strain in the solver. Made
test for if a particle is stressed based on its surface normal (and ofc
if its a surface particle). This behavior is tested. TODO: Test movement
under stress, and check if the values generated by the solver is
correct.
StressedSurface interaction implemented and thurely tested. Had to go by
checking components of surface normals to solve the issue. Ton of bugs
related to it, all of which should be fixed. All tests pass.