GUID.js: set a GUID cookie for unique users throughout a web application session

This plugin is intended to be used in the context of a web application where you want
to trace the path of a user through the page and how bandwidth and performance of the
application inhibits the user from his usual workload in an application.

The technique used in this case is checking wether or not a UUID has been set for the
sesssion as a cookie. It is intended to be used as searchable entity in the later
beacon analysis phase.

Configuration for this plugin may look like this:

```javascript
BOOMR.init({
	GUID: {
	      cookieName: "myCookieName"
	}
});
```

You may use the cookie name as the unique key to search for in your beacon data.
committed a change accordingly.