Replaces Lists with Sets, removes Study from signature.
Fixes warning about method signature.
Merge branch 'features/CHERKASY-implement-api-calls' into features/cherkasy-implement-observation-calls2
Implement observation tests.
Make .travis.yml use matching core-api/db
Fix maven cache usage on travis
Add empty UrlMappings file
Observations tests: remove some redundant allOf()s
Merge pull request #15 from thehyve/features/cherkasy-implement-observation-calls2

Features/cherkasy implement observation calls2