Bugfix: Password enforcement for public links

Password enforcement for public links, which can be adjusted on a per-role basis, wasn't properly reflected in the UI.
We have made the necessary adjustments to only enforce passwords for public links with the permissions that require a password according to the backend settings. 

https://github.com/owncloud/web/issues/6323
https://github.com/owncloud/web/pull/6749
