Re-added B-spline transformation for non-linear RT alignment in MapAlignerIdentification

Including updated tests.
Interesting! Looking a bit further into it there seems to be quite a huge argument on the internet on the pros and cons of const pass-by-value arguments which we shouldn't reproduce here. While I still would argue that their are certain benefits in making the argument `const` I will give you the Herb Sutter bonus here. What remains and is more important is the `const` method which should be possible after merging #1051. So please re-add it.