Message broadcasting to all ports from the worker

This PR intends to bring support for message broadcasting to all open ports within the worker.

Proposed API usage sample:

```js
var coll = new PortCollection();
coll.add(new Port({_portid: 42}));
coll.add(new Port({_portid: 99}));
coll.find(42) // Port instance with id=42
coll.find(99) // Port instance with id=99
coll.broadcastEvent('topic', {}) // broadcasts the message to all listeners, id=42 and id=99
coll.find(42).postEvent('topic', {}) // posts message to port with id=42
```

**This is currently work in progress, not to be merged until done.**