Add a global error display for when JS fails

[agjohnson]

Add some top level error catch and display an error to the user if our JS fails. Otherwise, things just spin forever or silently fail and the user doesn't have much of an idea what happened.

• Catch exceptions and add a toast element to explain to the user that there was an error

[agjohnson]

In our discussion on notifications, we talked about changing how the Django message default level messages show on the page. Currently, messages like "Log in successful" appear between the header and the page content and can eat up screen real estate. This is poor experience for a rather temporary message.

Instead, these level messages will be moved to a "toast" element (see FUI toasts documentation for an example). This would be a great spot to also show a top level JS error and it would blend in nicely there, not to mention can be triggered solely from JS.