Draft: Feature/quadrature volume average

What this MR does / why does DuMux need it:

This is a first draft how we could realize volume averaging by simply defining a quadrature rule on entity intersections

• Cherry-pick example of permeability averaging to demonstrate the simplicity of this approach
• Add PQ1Bubble scheme to also interpolate at quadrature points, yielding more accurate results.
• Maybe don't inherit from Dune::QuadraturePoint since there position() relates to local position.
• Use iterative solver