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>
In all places in this repo, I always use `{ }` for `if`, `else` statements. I think we should do the same here to make the code convention consistent.