- pulled export config up to abstract track exporter
- added rudimentary GPX support
fixed locale dependent number formats
- fixed possible NPE when there was no useful data in log to be exported (eg when there was no GPS fix)
- pulled writer logic into abstrct base class
- export height with cm
- removed empty entry in export format select list
GlobalPositionProjection: added "Ref" field
Added ant target for flightplot-lib jar
PositionEstimator: offsets and Z downside parameters added, minor fixes
Merge branch 'gpx_export'
Code style fixed and imports optimized
Removed empty item from formats list
Version updated: 0.2.3
GlobalPositionProjector: major cleanup
Export dialog bug fixed
Merge branch 'master' of https://github.com/DrTon/FlightPlot into export_config

Conflicts:
	src/me/drton/flightplot/FlightPlot.java
	src/me/drton/flightplot/export/ExportConfigurationDialog.java
	src/me/drton/flightplot/export/ExportManager.java
	src/me/drton/flightplot/export/ExporterConfiguration.java
	src/me/drton/flightplot/export/PX4TrackReader.java
	src/me/drton/flightplot/export/ReaderConfiguration.java
	src/me/drton/flightplot/export/TrackReader.java
use seconds instead of microseconds to specify export range
added labels to show formatted time range