Change the notifyDialog API a bit. Use a std::vector to keep track of
each payload item that needs to be fed to the resulting JSON.

Change-Id: If3229a88d2df5368e14290a0e80ebe6206780639
Reviewed-on: https://gerrit.libreoffice.org/44722Reviewed-by: pranavk <pranavk@collabora.co.uk>
Tested-by: pranavk <pranavk@collabora.co.uk>