Added initial GreenButton XML upload handling.
Remove old DataSet preview tests.
Skip GreenButton tests for now, until API is complete.
Allow a shorter form for specifying files for ingest.
Sort the files if given as a dict to ensure a consistent order.
Ensure that extra_rows will be set if no rows were requested.
Documented DataSet preview functions.
Add DataSet preview tests.
Merge branch 'master' of https://github.com/VOLTTRON/OpenEIS