Fix: Filters Q/gain control

[valentijnnieman]

As it stands the filters are not implemented perfectly. Some filter types use Q, some don't, and the same goes for gain. https://developer.mozilla.org/en-US/docs/Web/API/BiquadFilterNode At this moment we're only allowing Q input, we should allow gain input as well (and, if we really want to do it well, we can disallow Q or gain input for some types i.e. no Q input for low/high shelf filters).