Merge branch 'feature/exercise-grids' into 'master'

exercises/CMakeLists.txt

exercises/README.md

exercises/exercise-grids/CMakeLists.txt

exercises/exercise-grids/README.md

exercises/exercise-grids/exercise_grids.cc

exercises/exercise-grids/exercise_grids.input

exercises/exercise-grids/grids/grid_structured.dgf

exercises/exercise-grids/grids/grid_structured.msh

exercises/exercise-grids/grids/grid_unstructured.db

exercises/exercise-grids/grids/grid_unstructured.geo

exercises/exercise-grids/grids/grid_unstructured.msh

exercises/exercise-grids/injection2pproblem.hh

exercises/exercise-grids/injection2pspatialparams.hh

exercises/solution/CMakeLists.txt

exercises/solution/exercise-grids/CMakeLists.txt

exercises/solution/exercise-grids/exercise_grids_solution.cc

...ses/solution/exercise-grids/exercise_grids_solution.input

exercises/solution/exercise-grids/grids/grid_structured.msh

exercises/solution/exercise-grids/grids/grid_unstructured.db

...cises/solution/exercise-grids/grids/grid_unstructured.geo