Cleanup internal functions

[ldecicco-USGS]

1. Added note to function docs that properties NA will return all columns
2. Check properties against data in sysdata.rda. If it seems a property doesn't exist, go check dynamically
3. Make sure query errors on Bad Request.
4. Make sure empty returns come back with the attributes (they were getting dropped).
5. Cleanup some of the internal functions that were overly complex (due to not being refactored after other parts of the code were refactored)