Creates a temporary image file from a download from a URL

If you don't pass a file a temporary file is created in Temp Files folder. You're responsible for cleaning up the file after you are done with it.

You should check the filename that is returned regardless of whether you passed in a filename - if the file is of a different image type the extension may be changed.

public static Task<String> DownloadImageToFileAsync(string imageUrl,
	string filename,
	HttpRequestSettings settings)