Last code changes for 10.2.3

Addressed various issues and concerns:
- Replaced deprecated call to `toMilitaryGrid` (fixed #30)
- Put GPSLayer (i.e. my location, or ownship marker) above all layers (fixed #33)
- Removed import on demand for JUnit (better coding style)
- Removed references to other deprecated ArcGIS Runtime classes and methods

Once this pull request is merged, it will be tagged as the 10.2.3 release of Vehicle Commander.