Added config parameters to run EnPT in 3 AC modes: 'land', 'water',...

Added config parameters to run EnPT in 3 AC modes: 'land', 'water', 'combined'. Added some boilerplate code in atmospheric_correction.py which is to be replaced by separate AC calls for water and land surfaces later.

Signed-off-by: Daniel Scheffler <danschef@gfz-potsdam.de>