Add kernel plugin for Coherent Point Drift

This plugin depends on the C++ Coherent Point Drift library:
https://github.com/gadomski/cpd/. It adds a kernel function to run CPD
on two source files, and write out the results to an output file.

The result file contains the registered points. If the output file type
supports it, it also contains the point displacements in the
{X|Y|Z}Velocity dimensions.