Merge branch 'revert-cac1da4b' into 'master'

.gitignore

.patches/exercise-basic/exercise-basic.patch

...ercise-biomineralization/exercise-biomineralization.patch

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

.patches/exercise-dunemodule/exercise-dunemodule.patch

.patches/exercise-fluidsystem/exercise-fluidsystem.patch

.patches/exercise-fractures/exercise-fractures.patch

.patches/exercise-grids/exercise-grids.patch

.patches/exercise-mainfile/exercise-mainfile.patch

.patches/exercise-model/exercise-model.patch

.patches/exercise-properties/exercise-properties.patch

.patches/exercise-runtimeparams/exercise-runtimeparams.patch

exercises/exercise-basic/injection2p2cproblem.hh

exercises/exercise-basic/injection2pniproblem.hh

exercises/exercise-basic/injection2pproblem.hh

exercises/exercise-fluidsystem/2p2cproblem.hh

exercises/exercise-fluidsystem/2p2cproperties.hh

exercises/exercise-fluidsystem/2pproblem.hh

exercises/exercise-fluidsystem/2pproperties.hh

exercises/exercise-fluidsystem/README.md