BUGFIX Disable CMS preview for RedirectorPage (fixes #7127)

If the redirect is to an internal page, the preview iframe
will automatically load this new URL, causing the CMS edit
form to switch as well - effectively making it impossible
to edit a redirector page in the CMS as soon as it is saved
with an internal redirection target.
BUG: dependentPages grid field not showing necessary columns and their values.