In order to avoid a boatload of attributeBindings, I moved the root
element of the suggested-topics component into the template. Also,
autoformat their hbs files.
Testing info: https://www.scottohara.me/blog/2018/03/03/landmarks.html#using-screen-readers-to-navigate-landmarks
Additionally, flag modals with aria-modal=true to avoid the screenreader
accidentally escaping the modal. There's no need to ever toggle the
attribute to false, because we display:none the modal root when it's
closed.
