Added a speech rate

Took the liberty to help out with such a great app. Certainly came in handy for me the other day (https://twitter.com/neueanthony/status/393808090404904960) 

I added a UISlider to adjust the speech rate of the AVSpeechUtterance, which is something I am sure many of people have requested. 

I also made a few adjustments to the tint colour as the alertView that was being presented would cause the red tint to revert to blue. Not sure why, but setting the UIView's tintColor property seemed to solve that issue.