Sendmail module needs to be revised.

[UlrichB22]

The sendmail module needs to be revised.

These are the open topics:

1. The name of the website is not replaced correctly in the subject line of the email.
2. Some email providers require smtp_ssl for the connection, which has not yet been implemented.
3. The timeout parameter for the smtplib.SMTP class should be used to avoid endless hanging connections.
4. The /usr/sbin/sendmail function has not yet been implemented, and moin outputs a traceback when the mail_sendmail configuration setting is used.

I recommend removing the mail_sendmail configuration option. Please advise.

This is a preparation for #2056.