Feature/new materiallaw 2p

Current status

• The material law classes are built in a bit complicated way as a series of wrappers
• In order to evaluate a law you need the type of the law and the parameters
• Regularization is somewhat inflexible
• It's not possible to cache anything in the laws

What this MR does / why does DuMux need it:

• New class that gets policy template arguments instead of wrappers
• New fluidmatrixinteraction object that knows it's parameterization
• A single object that knows how to evaluate a law and can also cache things
• Flexible regularization that also allows e.g. for approximation / spline-interpolation in any part of the function

Fixes #319 (closed).

Special notes for your reviewer / TODO:

• !2249 (merged) Should be merged first.
• Add update function to update the parameters of a function (not implemented for now. Can be added later)
• deprecation in volume variables and other call sites (-> !2260 (merged))
• do the same for the interfacial area laws (non-equilibrium) (-> !2260 (merged))
• deprecate old laws
• adjust material law unit test to new laws
• implement brooks-corey
• implement twop default regularization for brooks-corey & vangenuchten
• reimplement weird "regularized" linear law (should be a separate law in my opinion since the entire curve is changed)
• reimplement heatpipelaw as example of a law that simply satisfies the interface (doesn't need to make use of TwoPMaterialLaw)
• Change all spatialParams to get rid of deprecation warnings (could be done in team)
• Use getters and setters for parameters (like before)
• Adapt 2p sequential headers
• Adapt plot material law to be able to use new style material laws
• adapt box interface solver
• adapt 2p incompressible local residual
• adapt flash headers and tests