Consolidate mountain shadow algorithms in S2 Idepix

[marpet]

Currently there are two different mountain shadow algorithms.

1. S2IdepixMountainShadowOp
2. MountainShadowFlagger

The first one is based on https://desktop.arcgis.com/de/arcmap/10.3/tools/spatial-analyst-toolbox/how-hillshade-works.htm
and was initially implemented by Jan.

[JanWev]

The second one was developed by Dagmar using the relative path calculated by the cloud shadow algorithm. It is only triggered if the cloud shadow is executed.