CanvasWindow.onClick() should have right click identification feature

[francesmcconnell]

We are building a Minesweeper game and realized it would be helpful to have a way to check the difference between right-click and left-click. We suggest that the MouseButtonEventHandler has an attribute or method that allows users to differentiate between different types of clicks. We are using the getModifiers method right now and having the users Shift-click, but we thought it might be more user-friendly to have a right-click option.