WIP Feature/generalize fvgridgeometry
What this MR does / why does DuMux need it:
So far this renames FVGridGeometry to GridGeometry for box, tpfa, mpfa and staggered.
** Things left to do:**
- deprecate FVGridGeometry property correctly
- open new MR with renaming and deprecation of all places where FVGridGeometry is used
- merge both MRs once they are both checked and reviewed (Timo says they should be separate to make the review process easier)
Special notes for your reviewer:
This now only changes and deprecates the aliases for the fvelementgeometry.hh files, the renaming and deprecation of all other instances (in the tests etc) will be done in a new MR.