Particle strength exchange scheme gives wrong solutions

[hjabird]

There is less viscosity then there should be. Due to incorrectly ordered arguments in internally called functions.

[hjabird]

Some work in commit dcf994d.
Argument ordering in internal calls swapped the viscosity and regularisation distance. This doesn't mean the code is actually correct however. Just less wrong.

[hjabird]

PSE seems to give correct solutions, only not a whole lot of viscosity transfer seems to happen. Perhaps this is to do with case setup?