[EnSoMAP] GUI improvement

[Andreas Janz]

In the various GUI windows/tabs some off the widgets should be replace:

• for all raster inputs use the QgsMapLayerComboBox widget, this way the user can select raster that are already opened inside QGIS/EnMAP-Box
• for all input or output files/directories use the QgsFileWidget widget

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All created output raster should be opened directly in the EnMAP-Box.