MAR-138: Updated documentation and release notes:

- Document the new xmpp_prosody_package parameter.
- Add the breaking change informaiton in release notes (although most
likely nothing will be really broken).

MAR-135: Updated documentation related to new environment variable for running handlers explicitly:

- Updated the usage instructions.
- Updated the release notes to include mention of breaking change.

MAR-131: Added support for specifying Python version in wsgi_website role:

- Introduced additional role parameter for specifying the Python
version.
- Updated tests to verify new functionality.
- Fixed existing tests to account for differences between Python 2 and
Python 3 - including changes to WSGI test applications.
- Updated documentation, documenting new parameter and fixing one
minor typo.
- Updated release notes.
- Bumped default version of Gunicorn/futures used.

MAR-133: Improve output for certificate checks:

- Do not produce warnings in case no certificates have been configured
for checking.
- Only send out mails about certificates that are about to expire.
- Include information in how many days a certificate is going to
expire.
- Include information on whether the certificates has already expired.

MAR-129: Added release note on breaking change in ldap_server role:

- The ldap_entries parameter can't use state "append" - since this was
part of the old m_ldap_entry module implementation.

MAR-129: Updated release notes:

- Added new section for next release.
- Covered the main breaking changes etc implemented.