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/database/trigger/trg_edit_page_content.sql

@@ -0,0 +1,4 @@
+DROP TRIGGER trg_edit_page_content ON edit_page_content;
+CREATE TRIGGER trg_edit_page_content
+BEFORE INSERT OR UPDATE ON edit_page_content
+FOR EACH ROW EXECUTE PROCEDURE set_edit_generic();