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

Could you please use the Control interface instead? Reaching into the internals and sending an EffectsRequest isn't very good.

```
EffectChainSlotPointer pChainSlot = m_pEQEffectRack->getGroupEffectChainSlot("[Master]");
EffectSlotPointer pEffectSlot = pChainSlot->getEffectSlot(0);
EffectParameterSlot pParameterSlot = pEffectSlot->getEffectParameterSlot(index);
ControlObject::set(pParameterSlot->getGroup(), QString("parameter%1").arg(QString::number(i)));
```
(checking for nulls along the way of course)