FFT block

OK so this is another way we could do the FFT block. It borrows heavily from the timeseries block, but is maybe a bit cleaner. Data goes in, FFT comes out when polled. Also you can query the FFT. 

![image](https://f.cloud.github.com/assets/149211/2493621/49d5dd4a-b29e-11e3-8b4e-d8b83f89e9dc.png)