Improve header/footer UI label (fdo#81227)

Indicate whether the header/footer being edited is only for the
first page, left pages, or right pages if applicable.

Change-Id: Ia38289503d0bae6cc6cef5917a47d5d25ca0f712
Reviewed-on: https://gerrit.libreoffice.org/10235
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>