Handle send intents

So I found this app in the play store and gave it a try.  It didn't quite do what I wanted, but when I discovered that it is open sourced here on github I decided to take a crack at modifying it.

My use case is that I want to be inside an app like Reddit Is Fun, click share on a thread, and send a gif link to gfycat to be converted and loaded.  I'm not sure that my solution is complete, but it works for me and I figured I would offer it as a proof of concept.  I think this would make gfycat better.

Let me know what you think.
Should use `TextUtils.isEmpty()`; will check both null and "".

Also, there is no "else" here if sharedText is null. Should call `showErrorDialog()`, otherwise if someone sends zero data the app will open and freeze. Might be best, actually, to just handle this below the entire intent parsing code (i.e., if `mGifUrl == null && mGfyName == null` then show error dialog).