Ensure author can only edit submission in 'new' or 'revising' states but editors can always edit.

Aperture's workflow requires that (non-admin) authors can only edit their submission either

• before it is submitted; or
• while revising a new version. Also, for all instance types, editors should always be able to edit the submission (presumably unless it is rejected, in which case there is no need to edit).

In all cases, only the most recent version should be editable.

Being able to edit a submission means both editing the form data, and (for customers such as Aperture that allow manuscript upload) editing the manuscript.