Correcting socketio handshake management and different timeouts.

According to https://github.com/LearnBoost/socket.io/wiki/Configuring-Socket.IO and to my understanding of socketio client side and socketio server side code, atmosphere-socketio sends a wrong handshake to the client.

### The initial situation in atmosphere server
There were two configurable timeout:
* **hearbeatInterval**: Defines an interval for the server to send ping event to the client.
* **timeout**: Defines the timeout that the client must respect before trying to reopen a closed connection.
They were sent in response of the initial handshake like this:
sid:**hearbeatInterval**:**timeout**:listOfTransports

### What the client expects
The client is expecting the following response to the handshake:
sid:**heartbeattimeout**:**closetimeout**:listOfTransports
* **heartbeattimeout**: Delay between two heartbeat before the client closes the connection
* **closetimeout**: The definition of **timeout** in the previous part

### The consequence
The heartbeat interval of the server is sent to the client as the heartbeat timeout making impossible to maintain the connection. Indeed, the server is not fast enough to send the ping before the client timeout and closes the connection.

### The solution
We just have to follow socketio documentation.
atmosphere-socketio was missing a third timeout: **the heartbeattimeout**
I added this timeout in atmosphere. This timeout is sent by atmosphere in response of the handshake, replacing the heartbeat interval.
Consequently, you can now set these 3 timeouts separatly while still making sure that the **heartbeatInterval** is greater than the **heartbeatTimeout**.