Integrate Tag view/edit pages in Manage menu

Currently tag_view_page.php and tag_update_page.php are designed as
standalone pages, so when accessed from manage_tags_page.php the "Back
to tag" button and the redirection after update take the user back to
tag_view_page.php, breaking the application flow.

Introducing a new manage_tag_view_page.php and that displays the menu
and passing the redirect page along allows a more seamless UX.

Fixes 0035228