[BUG] Parsing GNSS file requires Lat/Lon for column names

[jlmaurer]

Describe the bug
RAiDER should be able to ingest typical names for latitude and longitude in the GNSS workflow. Running with "Latitude" and "Longitude" currently results in an error

To Reproduce
Use the GPS workflow with a station file containing "Latitude" and "Longitude" as column names

Expected behavior
Should be able to parse generally-known lat/lon names

Desktop (please complete the following information):

• RAiDER installed via conda
• Mac OS