Update degree elevation and reduction functions

[orbingol]

As of geomdl v5.0.x, control points computation parts of the degree elevation and reduction algorithms are implemented in helpers module and they are working. On the other hand, the API call responsible for degree elevation and reduction (operations.degree_operations ) is still not working.

operations.degree_operations function should be updated with the correct algorithms and should be tested with B-spline and NURBS geometries.