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)

@curlymorphic

After some further testing... I think maybe we should reconsider using
the LR4 filter in the Eq. Or at least make it optional...

Currently, there's a noticeable loss of high-end, especially in
hats/percussion, with all filters disabled in the EQ... an EQ should
strive to be as transparent as possible when all gains are at unity.
Also it's probably kind of unnecessary - I don't think any of the
biquads introduce any kind of aliasing noise or distortion, the
implementations should be pretty solid, so I don't see much of a need
for an anti-aliasing filter, anyway.