Make participants view available for normal users.

The view removes the management UI (invite / remove participants) when the user has not enough privileges.
The link to the participants view is still protected, a link can be placed on integration level when needed.

I've also refactored the browser tests to use the newest ftw.testbrowser and the newest ftw.builder (umlauts in emails did change there).

@maethu can you take a look at this one?