Set default altitude override to 30 meters above ground.
Set default airspeed to 17 meters per second.

Do not do any projection before target coordinates have been set.

Initialize takeoff altitude at DEFAULT_OVERRIDE_ALTITUDE meters above ground.

Stop projecting destination

Fetch position from GLOBAL_POSITION_INT to get timestamped positions

Getters removed because these data should be fetch through position array.

Use position messages instead of gps ones in case of gps denial.

Now `setTargetCoordinates` always go through the desired point by updating
regulary the projected coordinates.
Function `loiter` is now defined for the purpose where `setTargetCoordinates`
was called with `going_through` parameter set to `false` (to loiter around a
point without going through it).