R1:3b1294cf4599

Store Phriction max version on Document, improve editing rules for editing documents with drafts

Summary:
Ref T13077. We need to know the maximum version of a document in several cases, so denormalize it onto the Document object.

Then clean up some behaviors where we edit a document with, e.g., 7 versions but version 5 is currently published. For now, we: edit starting with version 7, save as version 8, and immediately publish the new version.

Test Plan:
- Ran migration.
- Edited a draft page…