The preceding version picker should propose and accept only a restricted list of pages

Currently, when creating/editing a version page in a book, the picker provides all the pages of the wiki to be selected as a preceding version.

The preceding version field should only propose and accept pages:

• coming from the current book,
• that are actual version pages,
• not the currently edited version,
• and avoid loops (if V4 inherits from V3, and V3 from V2, V2 shouldn't be able to inherit from V4)