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/abbreviateNumber.js

@@ -0,0 +1,20 @@
+/**
+ * The `abbreviateNumber` utility converts a number to a shorter localized form.
+ *
+ * @example
+ * abbreviateNumber(1234);
+ * // "1.2K"
+ *
+ * @param {Integer} number
+ * @return {String}
+ */
+export default function abbreviateNumber(number) {
+  // TODO: translation
+  if (number >= 1000000) {
+    return Math.floor(number / 1000000) + 'M';
+  } else if (number >= 1000) {
+    return Math.floor(number / 1000) + 'K';
+  } else {
+    return number.toString();
+  }
+}