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].

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

Modified constructor (set time directly in constructor) / add getters for control points and their time corresponding

Edit file name spline_python.cpp to curve_python.cpp, in test.py edit TestSpline and test_spline to TestCurve and test_curve, edit all makefiles, make test 100% OK