Update license information for bsmtp.c based on GPG signed correspondence with Wietse Venema

As part of an ongoing license audit in Fedora, I reached out to Wietse Venema regarding the licensing of his smtp client code, which makes up the original core of bsmtp.c. Wietse wietse@porcupine.org replied quickly and attached a GPG signed license text consisting of a permissive license grant for that work.

This pull request updates the various bacula licensing files as well as bsmtp.c itself to reflect the proper permissive license of Wietse's work. It also includes a copy of his GPG signed license assertion in the src/tools dir.

I am happy to provide copies of Wietse's emails if needed, but they're very straightforward (I ask him what the license should be, he replies with the GPG signed license text).