Edit namespace, folder, file names from curve to curves

CMakeLists.txt

cmake

include/curves/CMakeLists.txt

include/curves/MathDefs.h

include/curves/bernstein.h

include/curves/bezier_curve.h

include/curves/bezier_polynom_conversion.h

include/curves/cubic_spline.h

include/curves/curve_abc.h

include/curves/curve_constraint.h

include/curves/exact_cubic.h

include/curves/helpers/CMakeLists.txt

include/curves/helpers/effector_spline.h

include/curves/helpers/effector_spline_rotation.h

include/curves/linear_variable.h

include/curves/optimization/OptimizeSpline.h

include/curves/polynom.h

include/curves/quintic_spline.h

include/curves/spline_deriv_constraint.h

python/CMakeLists.txt