updates sandbox component 'summarizer' to be compatible with latest opennlp-tools release

- adjusts opennlp-tools to 2.1.0
- adjusts Java language level to 11
- adapts code to comply with recent API of `POSTaggerME` from OpenNLP tools
- corrects indentation in many source files to comply with "2 spaces" style
- adds necessary resources required to run existing tests, via maven-download-plugin
- revives JUnit test to actually execute
- adjusts some code to be more modern style
31 files changed