Show a proper type for all variables

[fpagnoux]

As someone who contributes on a tax and benefit system, I can know the type of all variables, So that I understand better how the tax and benefit system works

---

For instance:

https://legislation.openfisca.fr/depcom

Sa valeur est de type FixedStr.

---

Implementation suggestion:

• Don't parse the column class name, but use the val_type column attribute
• Pursue the work done on openfisca/openfisca-core#551

[fpagnoux]

This has been solved some time ago