[processing] remove unused GDAL icons
[processing] use default icon for fillnodata
[processing] add gdal hillshade algorithm (addresses #7201)
[processing] add gdal slope algorithm (addresses #7201)
[processing] add gdal aspect algorithm (addresses #7201)
[processing] add gdal TRI algorithm (addresses #7201)
[processing] add gdal TPI algorithm (addresses #7201)
[processing] add gdal roughness algorithm (addresses #7201)
[processing] add gdal color-relief algorithm (addresses #7201)
[processing] add gdal interpolation (invdist) algorithm (addresses #7201)
[processing] add gdal interpolation (average) algorithm (addresses #7201)
[processing] add gdal interpolation (nearest) algorithm (addresses #7201)
[processing] add gdal interpolation (data metrics) algorithm (addresses #7201)