Timo Koch authored Apr 06, 2019 and Kilian Weishaupt committed Apr 24, 2019

The default flux variable cache filler helper classes for mpfa and tpfa
are actually specific for porous medium flow models, just like the cache
itself. This change moves them to a new header
porousmediumflow/fluxvariablescachefiller.hh
and deprecates the old classes and headers in the discretization folder.