add a preference setting to export compass heading in the gpx file (non functional yet)
compass heading is now being logged to the database (cleanup and testing needed)
compass heading is now also being logged in the track
export of compass heading to gpx implemented
adjust MockData to the new calls of track and wayPoint
onGpsStatusChanged now uses satellites that are used in fix for the bar graph, and disables buttons if there is no fix (0 satelites)
onGpsStatusChanged also updates the accuracy text box when there is no fix
Satellites are displayed in accuracy text box (used/visible)
Add a compass heading display to the Logger activity
compas now uses TYPE_COMPASS sensor since it provides meaningful accuracy info and has no problems when the phone is lying.
include compass heading value into waypoint list
sensor listener code now is only contained in SensorListener (to avoid duplication in GPSLogger)
some sanity modifications
various small style fixes
use AZIMUTH_INVALID in MockData and TAG in ExportTrackTask
some more clean up
removed some unused imports from GPSLogger
add compass accuracy to way- and trackpoints.
change sort order in waypoint list to descending (like this the last taken waypoint appears on top)
Merge branch 'compass' of https://github.com/chrisgee/osmtracker-android into chrisgee-compass
Minor changes to compass patch

- Minor label changes
- Minor code style changes (consistency)
- Restore "various_accuracy" string used in GPX export
- Ensure encapsulation of class fields
- Initialise waiting message for GpsStatusRecord otherwise it will display the placeholders until the GPS wakes up
- Keep logic of checking for a valid heading before returing the azimuth into SensorListener rather than having to implement it on the caller side