Rewrite DDM Collapsible in React

Consider doing the following instead to help keep all styles for a single selector in one place.

```scss
.ddm-collapsible__body {
  overflow: hidden;
  max-height: 0;

  .ddm-collapsible--mounted > & {
    -webkit-transition: max-height .3s;
    transition: max-height .3s;
  }
}
```