Modify the way distance indicators and LOD_LCZ are declared in the configuration file

[j3r3m1]

If not too much complicated, it would be nice:

1. to have a keyword in "grid_indicators" to decide whether or not the sprawl area layer should be calculated (instead of having it in the grid_indicator list
2. to add lcz_lod in the grid_indicator list and to replace the lcz_lod key value (used to define the number of levels) by a key word to set the number of lcz_lod levels (such as lcz_lod_nlev).

We can also think about other way to declare these two variables but the one proposed here might be an option