Class Scheme handling

[Benjamin Jakimow]

The EnMAPBox shoudl provide an interface that lists existing classification schemes to be used by other applications.

e.g. two raster classification files are knwon as datasources -> provide a list of all EnMAPBox(...).classificationSchemes() -> [list-of-ClassificationScheme]

see https://bitbucket.org/hu-geomatics/enmap-box/src/develop/enmapbox/gui/classificationscheme.py for Details of ClassificationScheme and ClassInfo

[Benjamin Jakimow]

closed Issue #165

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