Track material parameters

• compute conductivity and capacity during simulation + add to output
• rename soil parameters: more in line with the original van Genuchten naming
• switch to dataclasses from dict for Soil parameters
• compute convergence rate during coupled run
• add CLI / argument parser for coupled runs: allows for different input files
• fixed sign in flux computations
• switch to symmetric Dirichlet boundary conditions
• add minimum number of iterations to coupled runs if implicit coupling is used
• support different initial conditions for surface
• add script to visualize K and c for different values of psi

Closes #17 (closed)