Use nearest-neighbor resampling for image layer display

[forman]

Expected behavior

By default, geophysical data layers should be displayed using nearest-neighbor image resampling, so users can see the original, spatial grid cell extends in the images.

Changing the image resampling method for the 3D globe is possible since Cesium v1.39.
See Cesium issue #5846.

Actual behavior

All geophysical data layers are displayed using bi-linear interpolation.

Specifications

Cate 1.0