add an error dialog

Add a basic error dialog to replace our print() code. Fixes #693. This is something we can iterate on, to make it non-model.

![screen shot 2014-01-21 at 5 21 40 pm](https://f.cloud.github.com/assets/1269969/1970216/b3bc9ac0-8303-11e3-86ce-ab8b68ecd213.png)

@dinhviethoa