implemented microsoft autodiscover v2 and secure autodiscover.xml

Summary:
Added support for json based autodiscover v2 which currently only supports Protocol ActiveSync or rediret to the XML based autodiscover v1

In addition this change implements basic authentication for autodiscover.xml to support the autodiscover/authentication flow and protect users data (prevents email testing/scraping)

Reviewers: #autoconf_developers, machniak, vanmeeuwen

Reviewed By: #autoconf_developers, vanmeeuwen

Subscribers: #autoconf_developers, machniak

Differential Revision: https://git.kolab.org/D931