Return correct JSON types

[Eldelshell]

Currently, JSON data is made of strings only:

"cells": {
  "birthday": "1991-01-15",
  "name": "bar5",
  "id": "5",
  "lastupdate": "2020-05-08T20:48:25.090+02:00",
  "credit": "0.00",
  "age": "20"
}

In this situation, age & credit should be numbers:

"cells": {
  "birthday": "1991-01-15",
  "name": "bar5",
  "id": "5",
  "lastupdate": "2020-05-08T20:48:25.090+02:00",
  "credit": 0.00,
  "age": 20
}