Fix performance of get concepts by mapping

TRUNK-4452 made the underlying database call case-insensitive, which I suspect is negating any optimization that indexing provides and is potentially responsible for the mammoth slowdown in concept loading reported in this talk thread:

https://talk.openmrs.org/t/referenceapplication-2-5-is-not-compatible-with-isanteplus-module-we-developped-with-referenceapplication-2-3/10094/17

We should confirm that this is what is causing the performance issues, and, if so, fix it so we can do a case-insensitive search without losing the power of indexing, or provide both case sensitive and in-sensitive search options.

darius craigappl mseaton