Cleaned up and updated page picker a bit, allowing longer names to show,
clicking through to item without triggering popup, and updated to use
hidden attributes instead of styles.
Added phpunit tests to cover supporting entity-selector-templates
endpoint.
- Adapted existing page picker to be usable elsewhere.
- Added endpoint for getting templates for entity picker.
- Added search template filter to support above.
- Updated book save handling to check/validate submitted template.
- Allows non-visible pages to flow through the save process, if not
being changed.
- Updated page deletes to handle removal of default usage on books.
- Tweaked wording and form styles to suit.
- Updated migration to explicity reflect default value.
