* Moved URL-sharing-handling code to SharedUrlActivity.
* SharedUrlActivity prompts the user to confirm download of images from
the URL they specified, gets image URLs, sizes, downloads them to a temp
folder, runs the Media Scanner to repopulate the image DB, and then
opens a stock Android image gallery viewer.
* Current issue: images saved in the temp folder of the <external
storage folder root>/Pictures folder aren't appearing, despite the
gallery being prompted upon completing the async execution of the Media
Scanner.