Refactor UI test APIs

Refactored the UI test APIs:

- The UI APIs are used for creating users/groups/collabdocs/...
- Any JavaScript errors in the UI will be logged by CasperJS now, potentially giving more information about failing tests
- Exchange of information between UI and CasperJS happening through events
- More robust waiting for resources to get created
FWIW, the `/api/auth/logout` endpoints logs you out regardless of the authentication strategy you used to log in. It might be technically more correct to rename this to `logout`.