Add NeedlemanWunschGotoh Algorithm

[MarcelloPerathoner]

This implementation uses Gotoh's improvements to get O(mn)
running time and reduce memory requirements to essentially
the backtracking matrix only.

It uses a floating point token similarity score that yields
better alignment than a boolean match / mismatch score.

It also allows to specify gap opening and gap extension scores.

[djbpitt]

Although this is a Java patch, there seem to be (accidental?) changes to core_classes.py. These would need to be reverted before the patch could be evaluated and applied.