Experimental (incomplete) implementation of Websocket API

http://en.wikipedia.org/wiki/WebSockets

The Websocket API will allow for asynchronous communications with the Usergrid
API.

OAuth credentials are put in the querystring of the initial GET request since
the Javascript Websocket API provides no mechanism for specifying header
contents.

Once a connection is established, there are two mechanisms of usage.

Async Request/Response

The first is to simply access the API the same way as the REST interface
provides, except over the open websocket connection. The benefit is there is
much less overhead than with the REST API since there is no processing of
individual HTTP requests and authentication credentials are checked at the
time the websocket is opened as opposed to per-request as is necessary with
the stateless REST API.

Subscriptions

The second is to issue subscribe requests against entities and collections and
be notified asynchronously as those are updated. Subscriptions against the
activity inbox and message queue collections for either users, groups, or the
entire application allow connected applications to get realtime updates.

Connecting to an inbox or queue in the websocket url will automatically start
a subscription to that collection. For example, the following websocket url
will listen to a specific user's inbox:

ws://api.usergrid.com:8088/chatapp/users/johndoe/inbox

This is the real-time equivalent of making a regular REST GET request to:

http://api.usergrid.com/chatapp/users/edanuff/inbox

Usergrid listens to websockets on an alternate port than it does standard HTTP
requests. Although websockets can coexist on the same ports 80 or 443, Tomcat
and other Java servlet containers don't do a particularly great job of
handling open async socket connections despite what they claim. For our
purposes, we're using a bare metal Netty websocket server that listens on port
8088. This is going to be much more performant that trying to integrate it
into Tomcat and allows us to move the websocket servers onto different
machines.