Getting concepts by mapping should be case-insensitive

See: https://groups.google.com/a/openmrs.org/d/msg/implementers-archive/eJfHvW6LolI/Ob6HnJ2qSxIJ

Change org.openmrs.api.db.hibernate.HibernateConceptDAO#getConceptsByMapping so that it treats the code (and maybe the source?) as case-insensitive.

E.g. searching for a mapping to "org.openmrs.module.emrapi:Diagnosis Certainty" and "org.openmrs.module.emrapi:Diagnosis certainty" should be equivalent.