updates sandbox component 'mahout-addon' to be compatible with latest opennlp-tools release (#60)

- adjusts opennlp-tools to 2.1.0
- adjusts parent project (org.apache.apache) to version 18
- adjusts Java language level to 11
- updates to mahout-core in version 0.9 to mitigate several CVEs
- removes unused imports
5 files changed