Introduced "instancesParams" in file API

In the new configuration format (presented below) "params" becomes "instancesParams": an array that contains params for each single instance.
"shares" (that was an array) is substituted (both for "local" and "dropbox" configurations) by "share" (which is an object).

{
  "apiURI": "http://webinos.org/api/file",
  "instancesParams": [
    {
      "local": {
        "share": {
          "name": "mnt",
          "path": "/mnt"
        }
      }
    },
    {
      "local": {
        "share": {
          "name": "sd",
          "path": "/mnt/sdcard"
        }
      }
    }
  ]
}

Jira issue: WP-933