FieldPanels can now be marked as read-only with the `read_only=True` keyword argument, so that they are displayed in the admin but cannot be edited. This feature was developed by Andy Babic.
* Prevent choosers from failing when initial value is an unrecognised ID, e.g. when moving a page from a location where `parent_page_types` would disallow it (Dan Braghis)
The `insert_editor_css` hook has been deprecated. The `insert_global_admin_css` hook has the same functionality, and all uses of `insert_editor_css` should be changed to `insert_global_admin_css`.
The undocumented `wagtail.models.UserPagePermissionsProxy` class is deprecated.
If you use the `.for_page(page)` method of the class to get a `PagePermissionTester` instance, you can replace it with `page.permissions_for_user(user)`.
If you use the other methods, they can be replaced via the `wagtail.permission_policies.pages.PagePermissionPolicy` class. The following is a list of the `PagePermissionPolicy` equivalent of each method:
```python
from wagtail.models import UserPagePermissionsProxy
from wagtail.permission_policies.pages import PagePermissionPolicy
The `UserPagePermissionsProxy` object that was previously available in page's `ActionMenuItem` context as `user_page_permissions` has been removed. In cases where the page object is available (e.g. the page edit view), the `PagePermissionTester` object stored as the `user_page_permissions_tester` context variable is still available.
If you use `UserPagePermissionsProxy` in your code, e.g. the `user_page_permissions` context variable in an `ActionMenuItem` subclass as part of your `register_page_action_menu_item` hooks, make sure to replace it either with the `PagePermissionTester` or the `PagePermissionPolicy` equivalent.
