Change autosave delay to 30 seconds

It occurred to me that setting the autosave delay to 2 seconds makes the save button essentially useless: there's not enough time for students to use before autosave kicks in.  Additionally, I imagine students won't always want changes saved immediately, for example if they're playing around with the wording of a sentence.

For these reasons, I think it makes sense to change the autosave delay to 30 seconds.  Autosave will then wait 30 seconds after a student finishes making changes before saving.

@Lyla-Fischer Does that sound reasonable?