fix #10, add menu "toolbar" to display toolbar icons. Notes that in
R2018b, tools such as the zoom, pan, datatip, etc are no longer at the toolbar at the top of the figure window. These buttons are now in an "axes" toolbar and only appear when you hover your mouse over the plot. see: https://fr.mathworks.com/matlabcentral/answers/419036-what-happened-to-the-figure-toolbar-in-r2018b-why-is-it-an-axes-toolbar-how-can-i-put-the-buttons