Implement a class to plot the data loaded from the mat file

A first example of plotting of the walking data (x component of com::position::measured), synchronized with the visualization of the joints from the robot logger. Time (s) is plotted on the x axis.

Although the log is around 10-mins long, the walking is only active in a window between 100s and 200s and in another window between 300s and 400s. At the beginning, in the middle (oblique line) and at the end, the walking is not running.