FEFF Drone and task doc validation

[shyamd]

This is for @shyuep 's group.

Can the FEFF parsing be converted to a Drone that can:

• ingest any kind of FEFF calculation including extra files such as custodian.json
• injects structure metadata into the task doc
• performs some validation. This would be useful to make sure we're not storing bad FEFF calculations, for instance with spectrum with no data in it. Make sure the SCF is converged, etc.

Then deciding what data goes where should be performed in FeffCalcDb and the SpectrumToDbTask FireTask.