Parse GPS EXIF info

Given exif attribute, with info like:
- GPS GPSVersionID": "[2, 2, 0, 0]",
- GPS GPSLatitudeRef": "N",
- GPS GPSLatitude": "[0, 0, 0/100]",
- GPS GPSLongitudeRef": "W",
- GPS GPSLongitude": "[0, 0, 0/100]",
- GPS GPSAltitudeRef": "0", => above sea? under sea?
- GPS GPSAltitude": "0/50",
- GPS GPSTimeStamp": "[22, 48, 5]", <= is this UTC and/or GMT?????
- GPS GPSDOP": => NO?
- GPS GPSProcessingMethod": => NO?
- GPS GPSDate": "2018:08:11", <= Again use for GMTish?
- Image GPSInfo": =>NO

Determine:
- Simple decimal GPS location
- Altitude
- Geocode (city, state, country)
- Real timezone (from geocode or differential between EXIF & GPS time), real time stamp - possibly use it towards mtime - since normal exif time is local but no tz specified

Note: split from #2

Start from the EXIF attribute input described in the issue and trace how media metadata is currently handled. Clarify the expected decimal coordinates, altitude interpretation, geocoding, timezone, and timestamp behavior before implementation; done means these GPS fields have defined, tested results.

Written by the indexing model from the issue text.