wrapper functions for cut and flow solvers

[baugetfa]

I proposed to add wrapper functions for the cut and flow analysis (they are the ones I used for the publications)

• added 2 wrapper functions for the cut and flow analysis in solver_wrapper.py
  • one for cut and flow with the pure hydraulic solver
  • a second for the solute and water solver
• added also two python script examples for each case (I am preparing a jupyter nb)

Remark: working on it I realize that the code in wrapper is pretty hugly and can be optimized.

• there are also some minor typo correction in math in docstrings

[pradal]

This is quite big and I need to discuss to understand the change.
So merge it if it is needed but difficult to me to have an opinion

[baugetfa]

I won't merge it without discussion with you. I keep the PR open.

[pradal]

Excellent!