Added checks for ownCloud

Adding checks for ownCloud with this pull request. Tested against a live system running ownCloud 6.0.3 with some fake credentials "admin:admin" to check also the auth plugin.

An example version string of the status.php is the following:

``{"installed":"true","version":"6.0.3.1","versionstring":"6.0.3","edition":""}``

See also: http://demo.owncloud.org/status.php

Unfortunately i'm not really sure if the tests 006751-006753 are implemented correctly. If the auth plugin is successful the following is shown:

``Default account found for 'ownCloud' at /owncloud/remote.php/webdav (ID 'admin', PW 'admin'). Generic account discovered..``

but the following two tests for caldav and carddav are not shown.

Another question is why the "ownCloud WebDAV file upload detected (pass protected)" text is not shown when the authentication is failing.

Any hints about this two issues are welcome. Thanks.