Introducing CardDAV into core

apps/dav/.gitignore

apps/dav/appinfo/database.xml

apps/dav/appinfo/info.xml

apps/dav/lib/carddav/carddavbackend.php

apps/dav/lib/rootcollection.php

apps/dav/tests/unit/carddav/carddavbackendtest.php

...ests/unit/connector/sabre/BlockLegacyClientPluginTest.php

...tests/unit/connector/sabre/DummyGetResponsePluginTest.php

.../dav/tests/unit/connector/sabre/MaintenancePluginTest.php

apps/dav/tests/unit/connector/sabre/auth.php

...v/tests/unit/connector/sabre/copyetagheaderplugintest.php

...av/tests/unit/connector/sabre/custompropertiesbackend.php

apps/dav/tests/unit/connector/sabre/directory.php

.../tests/unit/connector/sabre/exception/invalidpathtest.php

.../dav/tests/unit/connector/sabre/exceptionloggerplugin.php

apps/dav/tests/unit/connector/sabre/file.php

apps/dav/tests/unit/connector/sabre/filesplugin.php

apps/dav/tests/unit/connector/sabre/node.php

apps/dav/tests/unit/connector/sabre/objecttree.php

apps/dav/tests/unit/connector/sabre/principal.php