Split out the KL Gaussian Mixture Reduction implementation function

This MR moves a bit of code around

QuickCloseMultiComponentMerge was including

• Simple functions for performing the calculation needed for a "Kullback-Leibler approach to reducing the Gaussian mixture"
• An implementation for allocating aligned dynamic arrays (size not known at compile time) that are passed to functions that need/want to assume aligned

I splitted these in other files. Ideally on the near feature we could try to write some tests and see how they can be improved . The alignedDynArray could be written a bit better in C++17 given lib support (for example gperftools where we get the tcmalloc supports "over-aligned allocation operators" from 2.6.2 )

Mentioning @amorley