Use first mapping if duplicated
We're getting duplicate mappings for CamSiS inst id to Lookup inst id for "CL" and "ED". The actual issue is incorrect data in jackdaw table is getting populated to inst-mapping API.
This is a hack to the sync tool that in addition to providing a warning of these duplicates also swaps behaviour to use the first (correct College mapping) instead of the latter (Classics and Education) mapping.
So a workaround until source data is corrected, but with a worthwhile warning added.
Part of #4 (closed)