Use email from git as From-address, clean up not needed stuff

- Removed attempt to get human readable name from the OS/PW database
- Made SMTP auth optional
- Removed SMTP-TLS
- Provide proper fallback when we cannot find a committer email
Added size limit to change emails

If size is more than 20MB we do not send any diffs
If size is more than 10MB we do not send HTML diffs
Flipped condition on SMTP password sending.
Added debug script to easily test changes and to have a sample of a debug run ready.
Reduced mail size to 10MB (plain-text)/5MB (HTML) to avoid getting filtered out by sourceforge's mailer daemon.

 Added a debug-flag that prints commit messages to Sdt-out instead of sending it via SMTP.

  Filtered out bogus "Unexpected:" mails when a ref was updated.
  GitHub does not allow us to run the script on their servers, so we have to
  mirror their repository. That pulls in remote tracking refs as well, and we
  don't want update notifications on them.

  Added specific message-handlers for pull requests to track their creation and
  their merge time.
Fix RegExp for pull requests