Fixes to get atc working again

This Pull Request contains a few fixes that have been cherry-picked from Connexions/atc#github . This PR will probably be tested by interns in a day or so.

Test: OPF comments
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1. Load Editor
2. Open and close books
3. Save all
4. [x] Reopen and make sure book changes are saved

Test: Overridden titles
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1. Change a title in the Book ToC (module title and chapter title)
2. Wait until autosave occurs
3. Browser refresh
4. [x] verify new title is still in the ToC

Test: Increasing Drop Zones
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1. Drag a ToC element and try to drop it:
  - [x] on another book
  - [x] on a chapter in the same book (should be a move)
  - [x] on a chapter in another book (should result in "Copy of ...")
  - [x] between 2 root elements
  - [x] between 2 root elements of another book
  - [x] after the last child of a chapter

2. Verify there is:
  - a large wide grey box when dropping **onto** something
  - still a thin wide grey box when dropping between 2 things (or appending after the last element)

Test: Reducing the number of Reparses
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1. Open a simple (no math or images) book
2. [x] Verify the "Save All" button does not get enabled
3. Make a ToC change
4. [x] Verify only 1 commit occurs (by looking at the github commit history)
5. Change a piece of content
6. [x] Verify only 1 commit occurs