[docs] draft for an upgrade guide from 2.4 to 3.0
different error for nop public parent
do still display publish button if not published successfully
Instead of a bright red for unpublished, use a light gray
Merge pull request #2814 from Chive/docs/upgrade

[docs] upgrade guide from 2.4 to 3.0
increase queries for edit mode
Merge pull request #2831 from digi604/fix-2821

Fix #2821 (pending pages no error messages)
fixes #2827
cleanup
fix tests
Merge pull request #2835 from digi604/fix-2827

fixes #2827 (moving public pages to unpublished parents)
Add JSON MIME types to HttpResponse in resolve() per digi604's direction

This fixes an issue where the side frame causes redirects to non-sensical URLs of the type: `http://127.0.0.1/en/<html><body>en</body></html>` or similar.
fixes correct descendants language
More updates
fixes #2834
fixes #2833
Merge pull request #2837 from mkoistinen/json_mime_type_for_2788

Add JSON MIME types to HttpResponse in resolve() per digi604's direction
Now using dashed outline 'ghosts' for non-existent titles, nice!
Merge pull request #2838 from digi604/fix-2834

Fix 2834 (page tree expansion preview link)
Merge pull request #2839 from digi604/fix-2833

fixes #2833