Generalise LArCalibValidation code to work also against references stored as LArFlatConditions object

Hi @pavol,

as discussed over coffee, here is my suggestion how to re-enable the templated LArCalibValidation-code with some of it's references stored as COOL-inline data instead of a LArConditionsContainer.
With this changeset, we create the payload of the complete-container on-the-fly from the flat-version as temporary objects, but only on a per-channel basis as needed.