Eq plugin

Initial pull request for the native EQ plugin, #1376 

![image](https://cloud.githubusercontent.com/assets/7412852/5425560/4ecbfbbc-8314-11e4-9a7e-334e7910f87e.png)

> Well if you want a counter-example, look at Fons Adriansen's 4-band
> parametric - it has freq, bandwidth and gain for each filter. The
> bandwidth there works as smaller = narrower, larger = wider. That seems
> the most intuitive approach to me.

Changing it to bandwidth then :)