More flexible tab layout

[aeberhart]

The tab layout currently allows showing array elements in tabs:

{
  "type": "array",
  "layout": "tab",
  "title": "test",
  "items": {
    "type": "object",
    "properties": {
      "name": {
        "type": "string"
      },
      "version": {
        "type": "number"
      }
    }
  }
}

produces

This raises the following questions and issues:

• The numbering is a bit "computer science like" by starting with 0 instead of 1
• One option could be to allow this layout for large nested objects, where each property with its subform gets displayed in a tab