[Import Spectral Profiles] improve default field mappings

[Andreas Rabe]

After I added an ASD profiles, my attribute table looks like this:

When now adding an ENVI Library, the default mapping looks a bit random:

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Also, what is the difference between “name” and “spectra names”?

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[Benjamin Jakimow]

resolves #1248

→ <<cset 655b189efa19>>

[Benjamin Jakimow]

1. that’s the standard QGIS way to assign source field names to the mapping table.
2. now only fields are suggested which either exists in the ENVI hdr or the csv file

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