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
I'm inclined to say we should probably leave this test out as it's part of the test refactor PR and would cause conflicts. It's only one file though so I'm fine with it staying in.