HUBDSM API: support band masks in VRTs created by Raster.saveAsVrt

[Andreas Janz]

@Benjamin Jakimow as pointed out in #414, the GDAL Data Model does not support band-wise masking.

The next best thing we could do is to store the band mask information (i.e. filename and band number) as band metadata. QGIS and GDAL won’t be aware of the masks, but when opening the VRTs via Raster.open, I can consider the band masks again and fully restore the Raster specification.

Its a bit like we are handling Wavelength information, which we also store as metadata. GDAL and QGIS are never aware of it, but our own algorithms are.

Nice?

[Andreas Janz]

That idea died :-)