Cleaning DaVinci tests and add new DaVinciExamples

Cleaning the DaVinci qmtests removing dependencies between DaVinciTests and DaVinciExamples. All the tests that provide examples for running DaVinci are now moved into DaVinciExamples while DaVinciTests is meant to have only unit tests.
The environment variable $DAVINCIROOT is reintroduced to access the Phys/DaVinci/options/DaVinciDB-Example.yaml database. This is just a temporary solution since in the end all the metadata infos of the input files used in the qmtests will be merged in the general TestFileDB, so the tests will not depend anymore on the Phys/DaVinci package.

Addresses #20 (closed) and provide some more examples for https://gitlab.cern.ch/lhcb-dpa/project/-/issues/102 and an example for running DaVinci with gaudirun.py required by #23 (closed).