Fix position updates on Android

Adding access to the vehicle hobbs meter

Firmware upgrade use QSerialPort

KML support for Polygons

Survey bounding rect intersection fix

Nope, it's microseconds alright. The autopilot I was testing with indeed only had 19 seconds of "armed" time.

README.md: Add new gstreamer example

Polygon: Create circular polygon

Structure scan: Photo count working, initial vehicle yaw support

PlanView: Solve KML error

Fix #5812
Show an error message when creating a KML without 2 items at least
Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

Specify altitude for guided takeoff

Structure Scan persistence and mission creation