Dispersion

addresses #320 (closed)

Only existing dispersion test is on dumux-lecture (Henry Problem)

• Implement compositional dispersion
• Implement thermal dispersion
• Scheidegger dispersion tensor
• FullTensor dispersion tensor
• guard against multiphase and non-box methods
• Add for tracer models compositional, and isothermal models
• Add compiler time catches for missing properties, and add warnings
• update dumux-lecture!170 (merged)
• Implement and test for TPFA constvelocity
• Add changelog entry for this new feature

To test:

• Thermal dispersion
• Compositional dispersion flux
• Scheidegger tensor from box velocity
• Scheidegger tensor from tracer velocity (constant)
• Open Tensor from input file vector
• Open Tensor from input file scalar