Instance history plot

[iamaya2]

• [x] Add a method for plotting the evolution of the makespan across steps of the solution for a given instance.
• [x] Add a method for plotting a histogram with the makespan of all instances, at a given solution step. Make it the final step by default.
• [x] Add a method for plotting the solver used at each step of the solution for a given instance.
• [x] Add a method for plotting a histogram of solver usage across all instances (and steps). Add flags for the plot and for displaying the information in the command line.