Also, a SystemFeedback model no longer has a `type`, it has an `intent`. This is
because SystemFeedback views have `type`, as well, and this prevents a naming
collision.

To reduce redundancy in tests

Doing so overrides the AJAX error popup

studio - removes the .is-fleeting class/animation that is handled by backbone's min/max time for notifications

studio - revises copy of server error notification to include a default message and removes associated actions from notifications

Model shouldn't know about things like close buttons, visibility, and so on

Hacking the Python, because our JS dependency management is borked.

It appears that one notification stealing focus from another causes some weirdness:
both clicking on a button on one view triggers the event on both views (the original
and the new view that stole the div). As long as the first view does *not* define
any click events, everything is fine -- this is the case for the saving notification.
I'll worry about the reason for this later; it has something to do with views
listening to models even after they no longer should be.

To create handy WarningMessage, ErrorMessage, and ConfirmationMessage classes

And delete `CMS.ServerError`