v1.8.0 * Call objstorage.add_batch() and objstorage.content_get() with a HashDict instead of single hash * Deprecate calling content_get with a single hash * cassandra: Add properties 'hosts', 'keyspace', and 'port' * postgresql: Return empty list in case of unknown metadata authority. * Refactoring, test and dependency maintenance * Document that Cassandra requires OpenJDK 11