Add option message_show_address_comments to show comments when displaying address headers.

[listerr]

This PR implements:

• a configuration option $config['message_show_address_comments'] = true;
• a user preference setting in Preferences -> Displaying Messages -> "Show comments in address headers"

Roundcube seems to over-sanitize when displaying From: headers, which can hide important information in the RFC5322 / RFC2822 comment part of the header.

Examples

RFC5322 / RFC2822 Header                                             | Before                          | After
---------------------------------------------------------------------|---------------------------------|------------------------------------------------------------------------------
Test User (test@domain.tld) <list@domain.tld>                        | Test User <list@domain.tld>     | "Test User (test@domain.tld)" <list@domain.tld>
Test User (via Test Mailing List) <list@domain.tld>                  | Test User <list@domain.tld>     | "Test User (via Test Mailing List)" <list@domain.tld>
Test User (via: Test, Mailing List) <list@domain.tld>                | Test User <list@domain.tld>     | "Test User (via: Test, Mailing List)" <list@domain.tld>
"\"test.user@domain.tld\"" (via Test Mailing List) <test@domain.tld> | "test.user@domain.tld" <test@domain.tld> | "test.user@domain.tld" (via Test Mailing List) <test@domain.tld>
root@domain.tld (Cron Daemon)                                        | (not displayed in RC 1.7.0)     | "root@domain.tld (Cron Daemon)" <root@domain.tld>
root                                                                 | (not displayed in RC 1.7.0)     | root
---------------------------------------------------------------------|---------------------------------|------------------------------------------------------------------------------

I don't think the last case of local-part with no domain name is strictly RFC compliant, but things like cron can often generate this header if the local MTA is broken, isn't configured with a domain, doesn't add a domain to From: headers missing a domain, for example.

The very neat new anti-spoofing warning feature isn't affected.

(I always enable $config['message_show_email'] globally and never allow users to turn it off.)

// Always show sender email address (not just name)
$config['message_show_email'] = true;

// don't allow users to change:
$config['dont_override'] = ['message_show_email' ];