Add acceptance tests for permalinks (AKA private links).

[SergioBertolinSG]

Currently this is not covered.

There is some info in owncloud/core#11732 and owncloud-archive/documentation#2986

[SergioBertolinSG]

@PVince81 after playing a bit with these links I don't see anything when requesting a GET to /index.php/f/FILE_ID using curl.

Is it possible to test this without the web ui? or this test would be better to be done in the selenium tests?

[phil-davis]

apiWebdavProperties/getFileProperties.feature has Scenario Outline: Retrieving private link

Need to see what else is needed...