Build properties

Here it is !

The underlying wiring is done: process -> data -> db.

I don't have data endpoint yet, it should make the subject of another PR I believe, That one is already big enough ...
The worst part about that change: that parameter is always given as an empty dictionary.

I left it at the end, because I thought for test purpose, we might want to insert properties during that call ... Turned out I didn't used it.

Too few tests or too many parameters ?