Signing scripts improvements

I think we can make the following improvements to the signing scripts we have in tools/signing:

• have a common config file to set tor-browser version, alpha/release, locales, paths, etc ... So that we don't have to update those variables in all scripts, and can use the scripts unmodified on the signing machines
• add a script to rsync the tools/signing directory to the linux and macos signing machines, to help keeping them in sync.
• update the macos notarization script to skip the already notarized bundles. So that if the notarization of a bundle fails, we can re-run the script and restart where it failed.
• add some scripts to rsync files between build machine, pkgstage, linux signer, mac signer, staticiforme
• add a script to run the macos-signer reverse ssh tunnel