GPS import function

[marklescroart]

Need ability to import GPS data from recoding on phone. This could go in this repo or possibly in ved-capture. Should generate gps.csv (or .npy) and gps_timestamps.npy in pupil folder.

[phausamann]

I think we should stick to the .pldata format which uses msgpack. Basically, it's just a serialized list of dictionaries, which in the case of GPS data would probably look like this:

[
    {
        "timestamp": XY.Z,
        "topic": "gps",
        "latitude": XY.Z,
        "longitude": XY.Z,
    }, 
    ...
]