Allow autoconfiguration by Mozilla Thunderbird and
other mail user agents using the same format.

This asks for a test at three levels:

1. Thunderbird as mail user agent
2. nginx as configuration web server
3. Dovecot and Postfix as MTA and IMAP servers

A new account has been created in Thunderbird
and the following check performed:

• nginx log entry
• Thunderbird configuration found reporting
• Thunderbird configuration parameters
• Thunderbird capability to receive mails with these settings
• Thunderbird capability to send mails with these settings
• Check if all looks good in the mail server logs