Remove unused 'release' method on TT data sets
Add isolation group IDs to TT data sets.
Generate isolated data sets from the crossfold task
Isolate data sets in different groups
Improve caching of specialized DAOs in evaluator

- Introduce common wrapping/cache logic for prefetching DAOs
- Use soft memoization for wrapper DAOs
- Retain event DAO reference in external eval job
Add commons-compress dependency (#556)
Use commons-compress for gzip compression (#556)
set encoding for JavaDoc
Enable XZ support (#556)
Test compression support in file utils
Add stream wrapping to compression mode.
Use compression modes more robustly in the engine loader
add missing license headers
Fix typos & stuff
Merge branch 'feature/elehack-eval-ds-cleanup'
Set 2.1-M3 as the version
Bump to 2.1-SNAPSHOT again
Basic lint support w/ JaCoCo reporting
Drop build dashboard
Make train-test data available in execution info (#600)