Merge pull request #13 from thehyve/SESI-111_dataset_validation

Sesi 111 dataset validation
remove created by comment
move error handling out of normal code path; return early
Fix bug in string comparison, slight refactor
some misc minor refactorings
add comment regarding not verifying https certificates
Merge remote-tracking branch 'origin/SESI-111_dataset_validation' into SESI-111_dataset_validation

Conflicts:
	opal-core/src/main/java/org/obiba/opal/core/service/validation/ValidatorFactory.java