style(ngRequired): mark when invalid

When using ng-required a red border on control is shown (styles added all 3 themes)

The styles will show only if the control is *dirty* and *invalid*, so to reproduce it you should first fill values on each field and then press `Clear ng-model`

You can try it with this [plunker](http://plnkr.co/edit/RN9Fry?p=preview)

![screen shot 2014-07-01 at 12 15 59 am](https://cloud.githubusercontent.com/assets/5034942/3439195/3e928638-00df-11e4-8d92-b72984d19146.png)