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.
If I do that, I get this: ```Warning [Main]: QObject: shared QObject was deleted directly. The program is malformed and may crash.```

I've read about a similar issue here[1] but I'm not sure if our warning is caused by the same concept.

[1] - http://blog.codef00.com/2011/12/15/not-so-much-fun-with-qsharedpointer/