* a new free function for the jacobian pattern accepting a container
  of dof dependencies

* todo: use common init routine for all FF tests to set epsilons

* user can now use StaggeredFVAssembler again instead of
  MultiDomainAssembler
* Wrapper class that inherits from MultiDomainAssembler, easier to use
* no explicit specification of coupling manager for uncoupled problems required
* move domainIdx from FVGridGeometry to coupling manager

* Add cell center of face specific auxiliary FvGridGeometry classes
   required for the multi-domain framework

* to make compatible with multidomain coupling stencils

* Make available for inheriting classes

* get the values for parallel and normal velocities directly in the
  fluxVars and not during the update of the faceVars
* this is necessary in the context of coupling when the velocities on the
  boundary shall be inferred from the other domain
* the gridFaceVars  are initialized (and thus updated)
  before any coupling context can be bound so this update step
  must not depend on some coupled context

Feature/1d3d richards2c 1p2c test

See merge request !831