Add socio eco indicators

[OlivierCoen]

Here is a first version of the socio eco indicators.

Caveats:

• The formula "Evolution du montant des revenus" and "Nombre de sources de revenus par ménage" were not implemented because the corresponding columns do not exist in the available datasets
• For "Indice de patrimoine" ("Material assets index"):
  • the limit at 24 asked was not implemented yet, because it would necessitate to duplicate the formula (with if... )
  • everything was divided by the number of households (little simplification)