Added Import for Temparature and Cadence from Garmin (Dakota 20)

Data is stored like that:

<trkpt lat="48.215245670" lon="16.487653144">
    <ele>138.570000</ele>
    <time>2014-12-19T08:00:10Z</time>
    <extensions>
        <gpxtpx:TrackPointExtension>
            <gpxtpx:atemp>14.400000</gpxtpx:atemp>
            <gpxtpx:hr>92</gpxtpx:hr>
            <gpxtpx:cad>36</gpxtpx:cad>
        </gpxtpx:TrackPointExtension>
    </extensions>
</trkpt>