Package postfix-html: Information

- Updated to 3.6.2.

- Removed notes about mynetworks_style from COMPATIBILITY_README.
- Changed postfix(1) to point to packaged version of COMPATIBILITY_README.
- post-install: silenced messages about unused erroneously packaged (in
  previous versions) files /usr/libexec/postfix/main.cf and
  /usr/libexec/postfix/master.cf .
- Changed default value of smtpd_relay_restrictions option to be:
  + independent of compatibility_level option value;
  + compatible with postfix < 2.10.

- Updated to 3.6.0.
- /etc/postfix/main.cf: set compatibility_level=3.6 for new installations.