Include no-snow classified pixels in "snow detected under clouds" QCFLAG for LIS 1.11 FSC

On LIS v1.11 (and previous versions) bit 4 of QCFLAGS ("snow detected under thin clouds") is only raised on pixels under clouds, classified as snow pixels after the dedicated snow pass.

A better definition of this flag would be : "pixels classified under clouds", including pixels classified as no-snow by LIS pass2.

Minor additional change : rename "snow detected under THIN CLOUDS" as "pixels classified under CLOUDS", since the flag is not calculated only under thin clouds but under all clouds (condition maja_cloud_mask_file > 0).