Concept for SF extract operation

[MichaelHuth]

There is currently an extract operation implemented for SF that extracts the one dataset from datasets.

For further extension the complete operation can have a API like:

extract(dataset, datasetIndex, arrayRowIndex, arrayColIndex, arrayLayerIndex, arrayChunkIndex)

The latter arguments allow to extract from an array.

extension with ranges:

extract(dataset, [datasetIndexStart, datasetIndexEnd], [arrayRowIndexStart, arrayRowIndexEnd], [arrayColIndexStart, arrayColIndexEnd], [arrayLayerIndexStart, arrayLayerIndexEnd], [arrayChunkIndexStart, arrayChunkIndexEnd])

This extension allows to specifify ranges that are then extracted.

[t-b]

Implement support for array index extraction without ranges, all optional. Needed for #2599. Support slicing, keep wave dimensionality.