fdo#79149 insert image dialog: rename Style to Frame Style

Change-Id: Ibb16ba76d2d7e98f5dc19dbcc82e80d8c08b334b
Reviewed-on: https://gerrit.libreoffice.org/12497
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>