Fix: issue6

Add in test_evaporation.py :

test_albedo_configuration_as_one_number()
test_albedo_configuration_as_one_grid()
test_seasonal_albedo_configuration_as_12_numbers()
test_seasonal_albedo_configuration_as_12_grids()
test_seasonal_albedo_configuration_as_mix_numbers_and_grids()
test_seasonal_albedo_configuration_with_missing_12_albedo_input_values()
test_albedo_with_wrong_domain()