Component cache logging improvements
Make sure assertions are enabled on tests
Enable assertions for integration tests
Clean up integration test running
Add assertion for FunkSVD columns
Delete old files from Maven testing

- Delete Maven invoker config files for integration tests
- Delete redundant lenskit-cli integration test
Decrease the memory use of non-full scored item accumulators
Merge pull request #576 from elehack/feature/elehack-test-assert

Test and assertion fixes
Merge pull request #577 from elehack/feature/elehack-accum-memory

Decrease accumulation memory use
Merge pull request #575 from kluver/kluver/clean-up-topN-evaluators

Clean up Top-N evaluators and fix NPEs.
Fix JavaDoc typo
Fix NPE in external eval job (closes #578)

If a test user does not have a training history, we should return an empty training history instead of null.