[cpp] add joint_trajectory_generator and nd_trajectory generator entities

CMakeLists.txt

include/sot/talos_balance/joint-trajectory-generator.hh

include/sot/talos_balance/nd-trajectory-generator.hh

include/sot/talos_balance/stc-commands.hh

include/sot/talos_balance/utils/common.hh

include/sot/talos_balance/utils/trajectory-generators.hh

src/CMakeLists.txt

src/joint-trajectory-generator.cpp

src/nd-trajectory-generator.cpp

src/utils/common.cpp

src/utils/trajectory-generators.cpp

unittest/python/appli_jointTrajGen.py

unittest/python/test_jointTrajGen.py