Graceful graph load failures

In the graph list:

* catch any img load failures
* hide the broken imgs
* hide the spinners
* set a background color, add a (somewhat) helpful message, and link to the graph profile

![Screen Shot 2013-03-15 at 9 41 37 PM](https://f.cloud.github.com/assets/494338/266221/c3f32d92-8dda-11e2-86b9-740557aa6a49.png)

In the graph profile:

* catch an img load failure
* hide the broken img
* hide the spinner
* set a background color and add a friendly background img

![Screen Shot 2013-03-15 at 9 41 50 PM](https://f.cloud.github.com/assets/494338/266222/c89109b4-8dda-11e2-870e-049336a781e4.png)

In an unrelated commit that I forgot snuck in here, added a handful of proper halts in failure cases.