HIG-ization of latest Persona search dialog

Fix some HIG issues with latest Persona search dialog
* frames to compartimentalize options
* wording of text
* status messages just above dialog buttons

Change-Id: I28d066e117cf1a49f2690ea44f5caca9cab9dd7d
Reviewed-on: https://gerrit.libreoffice.org/10936
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>