Attach original AJAX framework events to Snowboard in Backend

[bennothommo]

Replaces #1234, fixes #1233.

Instead of loading framework.extras.css, which appears to be excluded from the Backend, this PR hooks the necessary original AJAX framework events into Snowboard's events, allowing the applicable events to execute UI functionality such as data-attach-loading and the Stripe loader.

This is technically a stop-gap solution for now, since it doesn't emulate a full Snowboard request, so there's the potential for custom Snowboard event listeners to break if they are relying on Snowboard request information, but I'm not aware of that happening yet in core.

[mjauvin]

Nice!