* Started mass-refactoring of the current entity repos
* Rewrote book tree logic
- Now does two simple queries instead of one really complex one.
- Extracted logic into its own class.
- Remove model-level akward union field listing.
- Logic now more readable than being large separate query and
compilation functions.
* Extracted and split book sort logic
* Finished up Book controller/repo organisation
* Refactored bookshelves controllers and repo parts
* Fixed issues found via phpunit
* Refactored Chapter controller
* Updated Chapter export controller
* Started Page controller/repo refactor
* Refactored another chunk of PageController
* Completed initial pagecontroller refactor pass
* Fixed tests and continued reduction of old repos
* Removed old page remove and further reduced entity repo
* Removed old entity repo, split out page controller
* Ran phpcbf and split out some page content methods
* Tidied up some EntityProvider elements
* Fixed issued caused by viewservice change
Fixes#1662
Added a small block of logic to determine the correct URL to attribute to the cancel button on a given page create form.
If adding a book from a bookshelf, return to the bookshelf. If editing a book, return to the book. In all other cases, return to the full books list.
- Due to migration from Axios, Instances where we were sending FormData
were not considered and always converted to JSON which resulted in empty
JSON bodies.
Related to #1621
