Global refactoring - part 1...

- Removed the Imported/Exporter classes. Instead, used a more basic
ProxyMessenger class (which can receive and send messages) and its
subclasses: RemoteModel and RemoteController. First one is waiting a
messages from accordingly remote "controller" and emitting events.
Second one is sending messages (when call its methods) to accordingly
remote "model".
- Started implementation of RemoteTimeline.