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/formatNumber.js

@@ -0,0 +1,14 @@
+/**
+ * The `formatNumber` utility localizes a number into a string with the
+ * appropriate punctuation.
+ *
+ * @example
+ * formatNumber(1234);
+ * // 1,234
+ *
+ * @param {Number} number
+ * @return {String}
+ */
+export default function formatNumber(number) {
+  return number.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ',');
+}