Web App capability

Hello, Lucas!

I've just implemented a Web App capability to Shortly. I needed to include some meta tags on <head> and mess a bit with the CSS. I also included a new function to shortly.js so we could have a different behavior for mobile devices. It is possible to use it right on the mobile browser and, on iOS devices, add them to the home screen as a proper Web App.

I hope yo like it. Congrats for the great work

Cheers.
![screen shot 2013-05-12 at 23 11 52](https://f.cloud.github.com/assets/469519/493866/826d733a-bb72-11e2-865b-de1978062e25.png)