[package.xml] Add the file package.xml for catkin workspace

Add the example of Pyrene to the ddp-actuator-solver:
-Actuator model
-Cost Function (with torque, angle and velocity limits)
-Main for a single value of desired position or for a bag.

cmake changes to detect qpoases

Improve comments in CMakeFileLists.txt

[Major] Add "getLastCommand" method to simlplify API

_ add "getLastCommand" method to simlplify API
_ "solveTrajectory" now return last solved command, also to simplify API
_ Change convergence criterion for a correct one 'convergence when cost stop changing)
_ Add 2 more examples "Linear" and "Inverse pendulum" for future unitTests to come