Support raster image stacks

[jakimowb]

Raster time series products, e.g. observed or interpolated time series, are often stored as band stacks. In this case multiple bands can relate to the same date, like in the following table::

Band	Date	Meaning
1	2019-03-01	Blue
2	2019-03-01	Green
3	2019-03-01	Red
4	2019-03-02	Blue
5	2019-03-02	Green
6	2019-03-02	Red
7	2019-03-03	Blue
8	2019-03-03	Green
9	2019-03-03	Red

The profile visualization of such data could be enhanced by allowing to read specific only, e.g. to show the blue-band, but not the read and green band values.

The profile reading could be specified using two parameters:
start = the first band to read profile values from
step = band distance to read the next profile value from

Examples for the scenario in the table above:
start=1, step=1 (default), ll bands are read into the profile
start=1, step=3, read blue-band values only
start=2, step=3, read green-band values only
start=3, step=3, read red-band values only