CardDAV support for owncloud / sabredav plus external IMAP provider

redone to not replace the original carddav.php, but to use as an alternative

Based on the CardDAV code of ziirish there is an working CardDAV backend for owncloud / SabreDAV.
(see issue #80 / #76 / #47/ #71 )

to support my szenario there is a need to support external email provider with complete email address as loginname
Owncloud, can not handle Email adresses as usernamens. To use PHP-Push-2 in this requirement I've added some code