Rework some parts of the API
* Use Source object instead of String as Message Source
* Add prefix parser to be able to create the Source
* Cool way to check if a Source is a User or a Server
* Add some tests for this
* Update the Test Client
Add API for Channel join/part from Alix AND other Users
Add some fun to the Test Client (just to test previous commit a bit)
Fix considering itself as another User if Server sets a Prefix in the Join echo