Clean up double join.
Bug fixes: allow 'dimension' in MeasurementsController and show in serializer when present
Order measurements output, rather than grouping
Remove uniqueness test on MeasurementType name
Revert "Remove uniqueness test on MeasurementType name"

This reverts commit f53bf6b61cc6753b0065c9dd9583e055daf550c3.
Bug fix: validator now checks measurement_type
Unit test validator bug fix
MeasurementsController tests,

 including one flagged :broken, since validator is disabled
Unit test for measurement output ordering