Refactor Advanced Settings page to use Backbone notifications.
Prevent "saved" and "error" views from showing at the same time.

Previously the "saved" view was never hidden, even after more data was
edited. So if one field was saved successfully and then another was
not, we would find ourselves in the unfortunate situation of seeing
both views at once, leading to much confusion.
Hide "success" alert as soon as we start editing another field.
Merge pull request #242 from edx/peter-fogg/advanced-backbone-notifications

Refactor Advanced Settings page to use Backbone notifications.