Add roster add/remove contact functions
Created by: LNJ2
This introduces the new QML-side functions:
kaidan.rosterController.addContact(jid, name)
kaidan.rosterController.removeContact(jid)
Currently they are not used.
In my tests there was just one problem: The roster (UI) doesn't refreshes when a contact was removed, but whenever a contact was added. (Idk why)