GitLab

* Remove grid creation from executables.
* RichardsSimulation now builds its own Grid(Creator).
* Add new input key `parameters.file` to `parameters.xml` and remove all
    other keys of this section.
* Adapt other test executables.
* Add test for grid creation.
    * Add mesh files for grid creation test.
    * Add Python script for writing mapping files to be read by the
        test.
* Remove `grid-test.cc`.

The testing suite is generally not adapted to the new input scheme.
All tests of the main executable tests are broken.