Add method in FloatArray for fast fft-based convolution

[giuliomoro]

void FloatArray::convolveFast(FloatArray operand2, FloatArray destination, ComplexFloatArray temp1, ComplexFloatArray temp2)
maybe will require a temp3 as well

[pingdynasty]

Let's do this but as void FastFourierTransform::convolve(FloatArray lhs, FloatArray rhs, FloatArray dest)
(use lhs / rhs for left/right operands, and other for e.g. copy constructors).
Can it not be done with one temporary complex array?

[pingdynasty]

Actually it might be better to create a FastFourierConvolution class with all temporary arrays allocated in the create method.
Low priority.