EQ Rack

For more details, check: http://www.mixxx.org/wiki/doku.php/eq_rack

This PR still suffers from https://bugs.launchpad.net/mixxx/+bug/1335823. To reproduce it, check "Show All Effects" checkbox several times.
I would prefer here to keep the selected effect. You can just disable the EQ Effects by the enable CO 
Or the whole effect Chain by the chain enable CO