Massive JavaScript cleanup

- Use JSX for templates
- Docblock/comment everything
- Mostly passes ESLint (still some work to do)
- Lots of renaming, refactoring, etc.

CSS hasn't been updated yet.

js/lib/utils/anchorScroll.js

@@ -0,0 +1,22 @@
+/**
+ * The `anchorScroll` utility saves the scroll position relative to an element,
+ * and then restores it after a callback has been run.
+ *
+ * This is useful if a redraw will change the page's content above the viewport.
+ * Normally doing this will result in the content in the viewport being pushed
+ * down or pulled up. By wrapping the redraw with this utility, the scroll
+ * position can be anchor to an element that is in or below the viewport, so
+ * the content in the viewport will stay the same.
+ *
+ * @param {DOMElement} element The element to anchor the scroll position to.
+ * @param {Function} callback The callback to run that will change page content.
+ */
+export default function anchorScroll(element, callback) {
+  const $element = $(element);
+  const $window = $(window);
+  const relativeScroll = $element.offset().top - $window.scrollTop();
+
+  callback();
+
+  $window.scrollTop($element.offset().top - relativeScroll);
+}