Robust Moderation Queue and Iterative Editing

Issue Summary

Extend the features and robustness of the moderation queue to handle iterative editing of nodes (especially book pages). Requested improvements and additional functionality:

- configurable role permissions to edit any published book page
- display 2 views of the edited page
-- 1 view with current version of the book page (prevent disappearing content)
-- 1 view with edited version of the book page
submitted to the moderation queue (allow moderation by editor role)
- lock edited book page until editors have cleared the moderation queue
- visually identify for users that book page is unavailable for editing
till editors have completed moderation process (peer review)
- configurable if published book page should be permanently locked

This functionality would be a tremendous boon for Drupal sites where most of the activity is in the form of creating content, revising content, editing content, and publishing that content again.

A nice feature for editors would be:
- configurable notification for those in editor role about pending submissions for moderation