Final part. Here frmaddpage.ui is migrated, but to reuse the 2
other strings we need to shake up their original place in page.cxx

Now all the stings are moved to svx and occur only once in the code base.

Change-Id: I8b3942f96d43bf8d6f054c8410c3781bcefc3ccc
Reviewed-on: https://gerrit.libreoffice.org/46189Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>