Improved logging error handling in archive data importer.
Improved logging error handling in archive data importer.

Importer now raises a `CommandSyntaxError` rather than a `KeyError` when
a required input data item is missing, with a more helpful error
message.

HaroldMills/Vesper,HaroldMills/Vesper,HaroldMills/Vesper,HaroldMills/Vesper,HaroldMills/Vesper