Cleanup of ASAR mapper and corresponding Envisat class/module (by/with Anton). ASAR now adds incidence angle through new mechanism, going through small Nansat object.
ASAR mapper now calculates and stores SAR look direction, available as lazy operation on small ADS array
Fixed bug in ASAR/MERIS helper class Envisat: modifying hardcoded list of units affects subsequent calls to get_array_from_ADS function