Bug 32021: Don't show 'appear in position' for Pages

Bug 32021: Don't show 'appear in position' for Pages

The 'Appear in position' option isn't relevant for Pages, so we should
hide it when not adding or modifying a Page.

To test:

1) Add a new Page
2) Confirm the 'Appear in position' option does not show
3) Add a new News item or HTML customisation
4) Confirm the 'Appear in position' option DOES show

Sponsored-by: Catalyst IT
Signed-off-by: Caroline Cyr La Rose <caroline.cyr-la-rose@inlibro.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomás Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>