Support new "heading" tag from osmand tracker plugin

[blaueente]

Note that osmand now supports to track the heading in an "extension": (Needs to be explicitly enabled in the settings of the tracker plugin)

<trkpt lat="4X.XXXXXXX" lon="1X.XXXXXXX">

    <ele>XXX.XXX</ele>
    <time>2020-04-03T13:03:47Z</time>
    <hdop>7.504</hdop>
    <extensions>
        <speed>1.24</speed>
        <heading>233</heading>
    </extensions>

</trkpt>

1. Please support taking the direction from that.
2. To correct for phone/camera alignment issues, it might be possible to use the (smoothened) direction from the "next" point as a comparison and filter accordingly. This might enable to correct e.g. a constant offset, if a separate camera is mounted in a fixed angle to the phone, and it might be able to detect if both do not fit at all and throw an error. Or it might correct for magnetic errors due to large metal objects (car). Maybe a kalman filter could be useful here.