Adds 'proxy' taxon_concept's updated at from taxon_concepts_mview. to ensure that the cache is cleared after the mview is rebuilt if there had been changes to the taxon_concept
Account for the cases where there is no taxon_concept_mview for a given taxon concept (newly added taxon concepts)
Set proxied updated at to empty string if there is no m_taxon_concept
Merge pull request #101 from unepwcmc/hotfix_0.3.0

Adds 'proxy' taxon_concept's updated at from taxon_concepts_mview.