Add Capability to Provide a DocumentFile as the Download Location

[sathukorale]

Currently the only method that lets you initiate a download is DownloadManager.Instance.Download(string url, string downloadLocation, string fileName, string mimeType) method and the download location is passed as a string. Even though indirectly this location will be translated into the corresponding DocumentFile (with the help of the StoragePermissionsHandler.ICallback callback) a user/developer should be able to specify this directly. This is extremely relevant where internal storage is concerned (Since we cannot access the root of the PrimaryStorageVolume directly).

Ultimately there should be two options.

• DownloadManager.Instance.Download(string url, string downloadLocation, sting fileName, string mimeType)
• DownloadManager.Instance.Download(string url, DocumentFile downloadLocation, string fileName, string mimeType)