Smoothing without scipy

[kaalleen]

With these changes we can finally stop packaging scipy.

[bkmgit]

It maybe better to use an interpolation algorithim rather than dropping points.

[bkmgit]

Not sure if https://numpy.org/doc/stable/reference/routines.polynomials-package.html#module-numpy.polynomial would work. For piecewise smooth curves, cubic splines might be a good choice, though these would likely add other dependencies as developing good software for these can take time.

[kaalleen]

This method is very simple, but works surprisingly well for the few use cases we have though.
But of course I am open for other smoothing routines. I just want to get rid of scipy as this is a bit much to include it only for smoothing. To use as few dependencies as possible will definitely make our lives easier once the extension installation routine for inkscape has been updated.