Implement Gordon-Smith 2-pole oscillator

+ ensure that new audio path is completely out of the way when it is not enabled (e.g., extra buffer copies)
coding standard: "3.1.2.2 Class pointers must use C++ style casting:"

this code should be:
```
int16_t* inputFrameData = static_cast<int16_t*>(inputByteArray.data());
```

NOTE: I won't hold up this merge for this. We only recently added this standard and so there's some old code that doesn't follow it. But can you make a point of fixing this as well as any other places you see in your next PR.