Add yEd.app v.3.13

Cask added for yEd Graph Editor 3.13

From the website:
> yEd is a powerful desktop application that can be used to quickly and effectively generate high-quality diagrams. Create diagrams manually, or import your external data for analysis. Our automatic layout algorithms arrange even large data sets with just the press of a button.

Freely available here: [http://www.yworks.com/en/products_yed_about.html] (http://www.yworks.com/en/products_yed_about.html)