Update module information
- Bump version to 2.7-git
- Bump core module requirements to corresponding version
- Explicitly list dune-geometry dependence with version. Otherwise we may end up with an outdated version due to the sloppy dune-grid requirements.
- Depend on dune-istl. Its used in the tests for some time.
- Update changelog and adjust its layout
- Use dune-functions mailing list as maintainer information