Manipulate DOM in a Directive (Y072)

https://github.com/johnpapa/angularjs-styleguide/edit/master/README.md
- When manipulating the DOM directly, use a directive. If alternative ways can be used such as using CSS to set styles or the [animation services](https://docs.angularjs.org/api/ngAnimate), Angular templating, [`ngShow`](https://docs.angularjs.org/api/ng/directive/ngShow) or [`ngHide`](https://docs.angularjs.org/api/ng/directive/ngHide), then use those instead. For example, if the directive simply hides and shows, use ngHide/ngShow.

_Why?_: DOM manipulation can be difficult to test, debug, and there are often better ways (e.g. CSS, animations, templates)