No-data is incorrectly managed by various applications

Nodata management is incorrect.

• We need to distinguish no-data in source images (which is encoded in the source image metadata), and the no-data in output images produced by the applications
• Not only no-data shall be used in output pixels, but also set in the metadata of the output images
• It could be interesting to used NaN as no-data in images
• ExtractNormalVector handling of no-data in pixel neighbourhoods is incorrect