Update to make all class E_NOTICE safe, add page_content

- ALL classes are E_NOTICE safe as far as possible.
There might be some minor things left over which will be cleaned up in
further testing

- Added declare(strict_types=1); on all pages for trying to make all
calls strict

- Added page_content sub content to edit_page, with this some inner page
content with ACL can be set, eg for use with Ajax/JS calls with backend.
Also alias can be set so the control ajax pages can back reference to
the master page content setting. Currently only one back reference is
allowed

- Note that the PAGES array has no numeric indexes, but uses the cuid as
index

4dev/update/20190910_page_content/20190910_page_content_updates.sql

@@ -0,0 +1,7 @@
+-- 2019/9/10 update edit_page with reference
+
+-- page content reference settings
+
+-- UPDATE
+ALTER TABLE edit_page ADD content_alias_edit_page_id INT;
+ALTER TABLE edit_page ADD CONSTRAINT edit_page_content_alias_edit_page_id_fkey FOREIGN KEY (content_alias_edit_page_id) REFERENCES edit_page (edit_page_id) MATCH FULL ON DELETE RESTRICT ON UPDATE CASCADE;