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)

sohstationviewer/model/gps_point.py

@@ -12,3 +12,11 @@ class GPSPoint(NamedTuple):
     longitude: float
     height: float
     height_unit: str
+
+    def is_bad_point(self) -> bool:
+        """
+        Return True if this point is a bad point and False otherwise. A point
+        is bad if all its location data and number of satellites used are 0.
+        """
+        return (self.num_satellite_used == 0 and self.latitude == 0 and
+                self.longitude == 0 and self.height == 0)