[exercises] update coupling ffpm exercise

...hes/exercise-coupling-ff-pm/exercise-coupling-ff-pm.patch

exercises/exercise-coupling-ff-pm/README.md

...s/exercise-coupling-ff-pm/interface/freeflowsubproblem.hh

exercises/exercise-coupling-ff-pm/interface/main.cc

...ercise-coupling-ff-pm/interface/porousmediumsubproblem.hh

exercises/exercise-coupling-ff-pm/interface/properties.hh

exercises/exercise-coupling-ff-pm/interface/readme.md

exercises/exercise-coupling-ff-pm/models/CMakeLists.txt

exercises/exercise-coupling-ff-pm/models/params.input

.../exercise-coupling-ff-pm/models/porousmediumsubproblem.hh

exercises/exercise-coupling-ff-pm/models/readme.md

exercises/exercise-coupling-ff-pm/turbulence/params.input

exercises/exercise-coupling-ff-pm/turbulence/readme.md

...n/exercise-coupling-ff-pm/interface/freeflowsubproblem.hh

exercises/solution/exercise-coupling-ff-pm/interface/main.cc

...ercise-coupling-ff-pm/interface/porousmediumsubproblem.hh

.../solution/exercise-coupling-ff-pm/interface/properties.hh

...es/solution/exercise-coupling-ff-pm/models/CMakeLists.txt

.../solution/exercise-coupling-ff-pm/models/params_b_c.input

...lution/exercise-coupling-ff-pm/models/params_orig_a.input