WIP - Add an event routing mechanism.

[almet]

This is a work in progress. Do not merge (yet).

This is done in order to simplify how messages are sent and routed trough the
application.

eventrouter.js contains all the routing information, and the consumers should
send the messages to the router instead of the ports. Something like this:

this.router = new EventRouter("SidebarApp", this.appPort, this);
this.router.send("message");

The router object takes a reference to the routed object in order to call its
methods directly (rather than having to listen to events from within the
object).