Disabled scroll and focus for readonly elements.

Hey! 

This fix stop unexpected behaviour illustrated below.
![oct 11 2014 15 35](https://cloud.githubusercontent.com/assets/1904894/4602455/b930cbd8-513a-11e4-8643-bf4688f91629.gif)

The input I've clicked on was readonly. When it was clicked ion-content height became larger. I.e it was scrolled and was waiting for keyboard to show up. But since keyboard wouldn't show content height would stay incorrect.

Thanks!