Update multi-dataset input to be consistent with dashboard-framework and study-overview.

[samussiah]

{
  "type": "array",
  "title": "Schema for Multiple Input Datasets",
  "items": {
    "type": "object",
    "title": "Input Dataset",
    "required": [
      "data",
      "spec"
    ],
    "properties": {
      "data": {
        "type": "array",
        "title": "Data Array",
        "items": {
          "type": "object",
          "title": "Datum"
        }
      },
      "spec": {
        "type": "string",
        "title": "Data Specification Name"
      }
    }
  }
}