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

Add two getters to exact cubic (Number of splines + spline at index) / Modify unit tests for exact cubic

Fix problem in cubic hermite curve extended to any interval (not only [0,1]) / Added all conversion between bezier, polynomial, cubic hermite / All test ok

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].

Modif for spline deriv constraint to exact cubic : delete spline_deriv_constraint.h and modifications in other classes and tests