Implement a dialog to plot and export GPS data

Create a dialog with buttons to plot and export GPS data.

Show information about a GPS data point when user clicks on it.

#19 (closed)

tests/test_model/test_mseed/test_gps.py

 import unittest
 import math
 
-from sohstationviewer.model.gps_point import GPSPoint
 from sohstationviewer.model.mseed.mseed import MSeed