Modernize CMake configuration, formatting and add copyright checks
As mentioned at the PAC meeting Kepler was never migrated to the new CMake configuration style used in all other projects. This is not a blocker per se, but the old CMake configuration is not maintained anymore and this may cause problems in some cases.
With this MR I introduce
- the new CMake configuration
- code formatting (with the latest incarnation of the checks as in Gaudi)
- missing copyrights (supersede !30 (closed))