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
We shouldn't have function parameters like `user1`, as this causes the function to not be properly re-usable. It should be something like `expectedCreator`.