Not possible to reset atto autosave from JS

We have no current way to reset the atto autosave content.
It is currently cleared from within atto by listenign for a form submit event, but that event is not triggered when you call form.submit() - only when the submit button(s) are cancelled.

Recommend:

1. Make a new autosave event
2. Have existing submit listener trigger the auto save event
3. Allow anything to call it

This will allow JS forms to clear autosave.
May be even better to migrate the autosave component out of atto and allow it to take the relevant params and have events for save, resume, reset, etc. so that it's totally independent of atto.

Note: This affects assign at the moment.