Merge generic and specialized exchange methods

[m-Py]

Right now I have three functions that implement an exchange algorithm; 2x specialized functions that are speed optimized for maximizing the kmeans and cluster editing objectives, respectively, 1x a generic version that can maximize any objective function.

This means there is a lot of redundant code. It would be desirable to merge the three functions.

The difficulty in merging is that each of the three functions has need for different data structures that are generated and updated throughout the exchange method. I need to test if it is possible to merge the functions in a reasonable way despite this difficulty.