opens a dialog box from which user can choose to take online help or cancel it

Change-Id: I8c1278aab88d55901a65c38b15fcc8519360dc59
Reviewed-on: https://gerrit.libreoffice.org/31385Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>
Tested-by: Katarina Behrens <Katarina.Behrens@cib.de>