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
`waitForSelector`s like this one should not be part of the `casper.start` block. They should moved to the test they surround. In this case, the `waitForSelector` should be moved to the `verifyOpenAboutDiscussion` function. This would mean that when we have to call `verifyOpenAboutDiscussion` again that we don't have to repeat the `waitForSelector`