Add ability to choose Apple or Google emoji

Resolves/Fixes #35

I left Apple's as the default.  I invite the author to modify that default though ;)

The only problem is I noticed while finishing this one up that the master branch is out of date with the extension as it is on the Chrome web store.

P.S. I personally think this looks MUCH better

![](http://i.imgur.com/wCgeAdB.png)