Image brick updates

New features to test:

* Image width doesn't exceed the phone width
* When a 'bad source' is set, the image shows a picture frame with an X in it

![image](https://cloud.githubusercontent.com/assets/25212/4408982/ed80305e-44d8-11e4-9739-3fadc81fd3ba.png)

Fixes #1944

Should we update thumbnail.png to look like the new default image?