Convert insert error bars dialog to widget UI

Change-Id: Ie2fbcb0bacb968a784698908c8cc62f73a80cf32
Reviewed-on: https://gerrit.libreoffice.org/7219
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>