Export snapshots of flumped assets from flump exporter

Example .flump project file settings:

{
  "boundsSymbols": [
    "bounds_store_icon"
  ],
  "exports": [
    {
      "snapshots": {
        "store_icon": {
          "movieName": "idle0",
          "clipBoundsSymbol": [
            "bounds_store_icon"
          ],
          "clipBoundsOptional": true,
          "maxWidth": 187,
          "maxHeight": 153
        }
      },
    }
  ]
}