Add python bindings for method addActuationTask of inverse-dynamics-formulation-acc-force. Change name of method addTorqueTask to addActuationTask. Extend python example with UR5 robot with actuation bounds.

Add computation of average computation time in ex_3, slightly change configuration parameters for tests with Romeo.

The plot_utils.py file should be placed in the parent directory of the notebooks 

Adding and fixing the waist task for Pyrène.
The control is now working on both exercises.
Be careful to use joints and not frames when defining the Tasks and Trajectories. 
ie: use 'root_joint' and not 'base_link' for the waist.

Change the weights and gains: use the one of Pierre Fenrbach.

Change the create_empty_figure() method:
- Add an argument figsize to the method (to (7,7) by default)
- Add the figsize argument to the subplots

Try to add a task on the waist of Pyrène to fix the control (ex1). Not yet working.

Change a little plot_utils to fix the figsize.
Add an help for the installation process which will be added in the wiki.