Code clean-up
Add custom Spring Data REST configuration
Use links for Concepts in most places
Rename StudyVariables and StudyReferences 

- Without the Study!
Ignore vim swapfiles
Fix references to entity keys

- Fix study_variables references
- More sane naming conventions
Fix whitespace in XSLT
Disable hibernate debug output
Add variables mapping query + fixes to other queries
Move types to own package
Cleanup