a few fixes and performance increases:
* username autocompletes on click now instead of showing undefined
* an adjustable 'update interval' stops the huge performance hit by delaying events from firing until the user has stopped typing for a while
* nested controllers can cause issues because of prototypal inheritance if the models are not defined correctly... with ChatCtrl._chatMessage, this was the case. Modified it to fit in better with "best practices". See blog post here: http://jimhoskins.com/2012/12/14/nested-scopes-in-angularjs.html