Extend Debezium Schema Generator

• finish renaming of API/APIFormat occurences to use Schema instead
• add creation of directory structure per connector when creating descriptors: `postgres.json` --> `postgres/postgres.json`
• add configuration to add a schema filename prefix (e.g. `postgres.json` --> `debezium-postgres.json`
• add configuration to add a schema filename suffix `postgres.json` --> `postgres-1.9.0-SNAPSHOT.json`
• add some minor logging (available schema formats, selected format, processed connectors) and throw errors on failed state (no schema formats found, no connectors found)
• stop calling the Schema Generator in a separate process when called as Maven Plugin
• remove Oracle connector schema generation as it is not annotated yet