FSC upgrade for shaded snow

In particular sites, FSC is 0 whereas there is snow ! LIS 1.8 shaded snow detection detects the snow, but FSC is 0 due to FRE bands use.

• These pixels will be set to 100 on the FSC product in order to have the best snow coverage, which is used in annual synthesis.
• Bit 6 of the QCFLAG will be set to indicate that FSC 100% is not a real 100%.
• QCTOC formula will change to incorporate this flag : CI(FSCTOC) = max(0, 100 - (100 Fs + 30 FT + 50 FL + 25 FC + 25 FW))

on special case : #21 (closed)