Configurable start index and max length for Emoji application

I tested it a bit, it should work fine. I made this feature available only to TextViews.

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>
Oh I thought length was the length of the original string. But you're right, it makes more sense like that. I will fix that with the next commit and create a pull request for this and AOSP-style buttons. Thanks.