Graphic EQ Effect

Thiss PR adds a 10 band static equalizer based on Biquad filters. The implementation of the Biquad filter is based on @daschuer's iireqs branch.
I have put a flag inside pauseFilter() itself. Please tell me if this is the desired behaviour. https://github.com/badescunicu/mixxx/commit/8ce1b54885d637ad9a35ce82d9eded9ccb885ffd