Smoothing Elevation Data optained form GPX file

[wp99cp]

We should smooth the elevation data obtained from the GPX file/elevation server to remove outliers. Alternatively, we can drop them during the parsing process (if there are some nearby points in the path). In the worst case, we could fix the error by refetching the elevation of individual points.

There are at least two tours with such an Issue. One of which can be found here: https://github.com/ckolin/marschzeittabelle/blob/main/samples/app_extralong.gpx

The other one is of @maede97 throw the Tösstal.

<trkpt lat="46.7732856112" lon="10.4163604006">
	<ele>1863.8</ele>
	<extensions>
		<swisstopo:routepoint_id>1076989589</swisstopo:routepoint_id>
	</extensions>
</trkpt>
<trkpt lat="46.7737814192" lon="10.4154706754">
	<ele>46.8</ele>
	<extensions>
		<swisstopo:routepoint_id>805781812</swisstopo:routepoint_id>
	</extensions>
</trkpt>
<trkpt lat="46.7739153331" lon="10.4148229627">
	<ele>1820.8</ele>
	<extensions>
		<swisstopo:routepoint_id>678327115</swisstopo:routepoint_id>
	</extensions>
</trkpt>