fdo#80453 (part) Help button for insert random #

* Insert help button in dialogo
* HIG-ify dialog.

Change-Id: I839af28981e9bd980842e73e29bd6443f4154b86
Reviewed-on: https://gerrit.libreoffice.org/10944
Reviewed-by: Thomas Arnhold <thomas@arnhold.org>
Tested-by: Thomas Arnhold <thomas@arnhold.org>