choose Orientation source based on value accuracy

[ruleant]

choose orientation source :

• orientation sensor (deprecated)
• getOrientation (based on gyroscope and magnetic sensor), issue #41 (fast, but sometimes inaccurate)
• based on GPS data (slow)
• calculated from current and previous location (even slower)
• Combine sensors to get a raster and accurate value : calibrate sensors based bearing with GPS based bearing.
• use calculated orientation based on previous location as reference if GPS location is not available.
• test in real world conditions