Edit piecewise_polynomial_curve to piecewise_curve (make it more general using templates) / Add python binding for all types of piecewise curve / Edit std error thrown

Modification in bezier curve, now there is a T_min and T_max (Only T_max before). More logic for curve_conversion. Also modified split bezier curve : before bezier curve defined on [0,T] and we splitted it in ts => bc1 was defined on [0,ts] and bc2 on [0,T-ts]. Now, bezier curve defined on [T_min,T_max] is splitted in ts => bc1 defined on [T_min,ts] and bc2 defined on [ts,T_max].

Edit polynom to polynomial in all files. File polynom.h edited to polynomial.h and bezier_polynom_conversion.h to bezier_polynomial_conversion.h

change namespace spline to curve in include folder, rename folder spline to curve, change in the CmakeList.txt