Add callbacks for active and inactive

[callmenick]

A lot of people want to use this to toggle menus. A good idea would be to re-think the component JavaScript to have event callbacks that users can plug in to.

[Hlsgs]

+1 Also, i would move(and rename?) the .is-active class to the body or html tag as it's almost a give that the icon's state will affect outside elements. Thanks for this, by the way!

[Kedarnath-Rothe]

Please assign this issue to me