Modification in bezier curve, now there is a T_min and T_max (Only T_max...

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].