Landed 23 is a refactoring of Landed 22, to separate GUI and Backend code

Landed 23 is a refactoring of Landed 22, to separate GUI and Backend
code better to facilitate porting from Hamattan to Sailish and other
platforms. This commit is work in progress, and is focused on the GPS
functionality. Previously this was GPSApp. This is now split into
GPSBackEnd and GPSDisplay