removed support for concept mappings

unfortunately, Sesame / OWLIM Lite can't seem to handle evaluating this
at runtime, with query response times way beyond acceptable levels

thus we'll have to resort to pre-computing concept mappings and
rewriting the source data accordingly

This reverts commits f80983cec0fc2cce900d4ae13f276c4e86013e10 and
5ac01087ae97ef37eb72940613f405a18c77474a - effectively rolling back to
pre-v1.7
grouped observation count by source

this is in response to a downstream requirement - making this
configurable seems YAGNI for now