What this MR does / why does DuMux need it:
Use the same implementation for the coupling jacobian for all cvfe schemes
is the code you changed and/or the new code you wrote covered in the test suite? (if not, extend the existing tests or write new ones)
is the list of the header includes complete? ("include what you use")
all files have to end with a
\ncharacter. Make sure there is no
\ No newline at end of filecomment in "Changes" of this MR.