ENH: validation of configuration schema including unit tests

src/caosdb/configuration.py

src/caosdb/schema-pycaosdb-ini.yml

unittests/broken_configs/pycaosdb-indiscale-demo.ini

unittests/broken_configs/pycaosdb1.ini

unittests/broken_configs/pycaosdb2.ini

unittests/broken_configs/pycaosdb3.ini

unittests/broken_configs/pycaosdb4.ini

unittests/test_configs/pycaosdb-indiscale-demo.ini

unittests/test_configs/pycaosdb1.ini

unittests/test_configs/pycaosdb2.ini

unittests/test_configs/pycaosdb3.ini

unittests/test_schema.py