Introducing the first shiny stuff for our new event-based core backend

This adds a (very rudimentary) base class for events, and a (very rudimentary)
EventManager. The manager so far allows registering event handlers (even via explicit
methods, or by providing a QObject. In the latter case, matching slots will be automatically
registered (i.e. a method handleIrcEventJoin() will be registered as handler for
IrcEventJoin).