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 think we should hold a strong reference to the EQEffectRack. This ensures that it is not detested early elsewhere. 
You can user .data() inside the connect statement.