Entity Repo & Controller Refactor (#1690)

* 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

app/Exceptions/MoveOperationException.php

@@ -0,0 +1,8 @@
+<?php namespace BookStack\Exceptions;
+
+use Exception;
+
+class MoveOperationException extends Exception
+{
+
+}