support websockets for real time events

[mblackstock]

We may want to consider using atmosphere (https://github.com/Atmosphere) - it seems to play well with the spring framework and runs on Tomcat 7+

[mblackstock]

Extending #21, Application resources could be extended to own a web sockets stream as follows.

Add a thing subscription to an application stream

POST /applications/{appId}/sub
{
"thingId": thingId,
"filter": filter - "all", "thing-only", "following-only"
"query":query - query on the events that should be received
}

Get list of thing subscriptions

GET /applications/{appId}/sub
returns list of subscriptions
[ ... list of subscriptions ...]

Get real time web sockets stream

GET /applications/{appId}/stream
retrieves events in real time on all subscribed things on a web socket