Fixed incorrect accuracy assignment in Rinex3NavData from EphemerisGPS

[eugenyk]

We suspect that in Rinex3NavData::operator GPSEphemeris should be
accuracy = gpseph.accuracy;

Because

• gpseph.accuracy is never used during construction
• GPSEphemeris::accuracyFlag is short but Rinex3NavData::accuracy is double
  And because of description

double accuracy;     ///< SV accuracy (m)

short accuracyFlag;        ///< Accuracy flag (URA)
double accuracy;           ///< Accuracy in meters (from accuracyFlag)

Unit test with conversion check added

[masamitsutech]

Before this pull request can be reviewed for the next stable release, please update the branch to resolve possible merge conflicts.