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.
setCoefs() is not enough, since the old filter is still used for ramping. 
It looks like we need a new function to start a filter again from zero after a break. 
We need to ramp in the new samples, but without ramping out the old one.