remove cubic and quintic classes

[CMake] fix pinocchio detection

ref https://github.com/loco-3d/multicontact-api/issues/5

[Python] Add pickle support

Add serialization/curves header

Otherwise, this header is installed if BUILD_PYTHON_INTERFACE, and not
if INSTALL_PYTHON_INTERFACE_ONLY.

But if we want to be able to have binary packages for:
- the main curve package
- its bindings for python 2
- its bindings for python 3

this header will be installed in the 2 last cases, which will conflict.

In short: if we set INSTALL_PYTHON_INTERFACE_ONLY, there should be only
stuff installed in PYTHON_SITELIB.

[Python] Fix issue #32

Replace assert with exceptions - addresses #28

install header python/python_definition

Fix when t_min == t_max

Add API to get bezier waypoints and SE3 translation/rotation curves