Static 8 Band Master EQ 

This PR adds a static 8 Band EQ to the EQ Preferences. 
It can be later extended to a configurable Effect Rack, that is intended to setup before the gig, during sound check.  
For Mixxx 1.12 this should already cover the most common use-case: to equalize the sound of the sound-system. 

It is on top of the filter_effect PR

This is a preview to our LV2 branch where we can add EQs with 20 parameters or so. 
The idea was that we can pick 8 parameters of them, that are mapped to COs to have a smooth skin integration. All other parameters should be tweak-able by the preference pane. 

It think we need to do some refactoring to beautify this way. Any Ideas?