App structure API

This is a deliberately simplified (possibly too much) API to expose the app structure.

```json
{
  "meta": {
    "limit": 20,
    "next": null,
    "offset": 0,
    "previous": null,
    "total_count": 2
  },
  "objects": [
    {
      "modules": [
        {
          "case_properties": [
            {
              "enum": {
                
              },
              "field": "case_property_a",
              "format": "plain",
              "header": {
                "en": "Case Property A"
              }
            }
          ],
          "case_type": "ffff_case",
          "forms": [
            {
              "media_audio": null,
              "media_image": null,
              "name": {
                "en": "dddd"
              },
              "questions": [
                {
                  "label": "fffddfasdfasdf",
                  "tag": "input",
                  "value": "\/data\/zzzz"
                }
              ],
              "xmlns": "http:\/\/openrosa.org\/formdesigner\/2EEAA1B8-8779-4028-8723-8C42E5C6ED09"
            }
          ]
        }
      ],
      "name": "asdf",
      "resource_uri": ""
    },
    {
      "modules": [
        {
          "case_properties": [
            
          ],
          "case_type": "",
          "forms": [
            {
              "media_audio": null,
              "media_image": null,
              "name": {
                "en": "Untitled Form"
              },
              "questions": [
                
              ],
              "xmlns": null
            }
          ]
        }
      ],
      "name": "Untitled Application",
      "resource_uri": ""
    }
  ]
}
```