updates sandbox component 'mallet-addon' to be compatible with latest opennlp-tools release (#61)

- adjusts opennlp-tools to 2.1.0
- adjusts parent project (org.apache.apache) to version 18
- adjusts Java language level to 11
- updates to mallet version 2.0.8 to mitigate several CVEs, adds exclusions and related newer versions to mitigate CVEs
- adjusts some array declarations to comply with Java, not C, style
- improves resource handling of streams
- removes unused imports
7 files changed