[panel] Recursively resolve allOf property

[arntanguy]

This PR adds support for recursive allOf properties in JSON schemas, e.g

    "allOf":
    [
      {
        "type": "object"
      }
      {
        "allOf":
        [
          {
            "properties":
            {
               "type": "number"
            }
          },
          {
            "$ref": "/../../ref.json"
          }
        ]
      }
    ]

This is necessary to support the reorganized StabilizerTask schemas of jrl-umi3218/mc_rtc#95