Issue6

Modified  in evaporation.py : 
 - read_configuration_albedo()

Added 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()