title: Control file name of UIImage send with UIActivityViewController
body: <p>I'm sharing an image, along with a url and some text, with a <code>UIActivityViewController</code>. Everything works great, except the image file name is always 'Image-1' with no extension. In some cases this causes a big problem, such as in the mail app which won't open an image without an extension at all.</p>
  
  <p>The image is being generated by the application and exists as a <code>UIImage</code>.</p>
  
  <p>Is there a way to control the file name and add the correct extension to the image?</p>