Refactor UserData in the worker

This refactors the UserData object in the worker in preparation for adding in presence information. Specifically:

- Reduces the attributes for the UserData object to just userName, as that is the only one that is currently required (presence will be added in the next PR).
- Makes UserData responsible for sending social.user-profile messages
- Fixes some issues in the image urls. We should now always get a image on the button, and the default avatar image for the user (shown in the menu).
- Updates and fixes tests
- Fixes the expectations that some tests had on _currentUserData existing when their before/afterEach functions hadn't actually created it (partial fix for running tests individually)