Standard and Custom page templates are really not so different from each other. Standard pages are included by default in the CMS, and Custom pages are created by you. Until now, they've been kept in 2 separate places in the CMS - but no more.
Now, when you want to edit a page template, all you have to do is navigate to Content → Page Templates.
(screenshot here)
Here you'll find Standard pages, Custom pages, and even the Theme Layout.
Your favourite templates are still marked with a star and are the first ones you see on landing at this page.
