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)

Dave: a couple more things.

- Should the Q control for peak filters be inverted? Seems to me a bit
counterintuitive - increasing Q decreases bandwidth... I always turn it
in the wrong direction because of this.

- For the display widget: how about if you could control the Q/bandwidth
of each filter by using the scroll wheel while on top of the number?

- Analyzing: how about if you could toggle the display to IN/OUT
(current), IN only, OUT only? It's sometimes a bit hard to see the curve
when they're always overlaid, modes to show only in or out would help
with this. The current IN/Out labels could be used as toggle buttons.