RFC6764 - CalDAV discovery

[azmeuk]

RFC6764 defines SRV and TXT entries for CardDAV and CalDAV services discovery. It allows client applications to find the DAV endpoints path just by knowing the domain on which it is hosted.

Implementing DAV service discovery in GTG would allow non tech savvy users to configure synchronization without having to fill technical data about their server, only username, password and domain.

This would be a very minor improvement, but another step toward service discovery democratization.

edit: related python-caldav issue