LPS-39405 Display the add page tab based on the Add Layout permission
LPS-39405 Display the add page tab for any type of page.

The type of the current page should not prevent the user from adding other pages.
LPS-39405 Hide the add page tab when editing a page template.

Previous checking was wrong: even if the page is linked to a page template, the add page tab should be displayed if the user has permission to add more pages to that site.
LPS-39405 Check layout update and layout customization permissions to display the add application tab
LPS-39405 Rearrange permission logic
LPS-39405 Improve consistency of permission checking logic in the add panel