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/extract.js

@@ -0,0 +1,15 @@
+/**
+ * The `extract` utility deletes a property from an object and returns its
+ * value.
+ *
+ * @param {Object} object The object that owns the property
+ * @param {String} property The name of the property to extract
+ * @return {*} The value of the property
+ */
+export default function extract(object, property) {
+  const value = object[property];
+
+  delete object[property];
+
+  return value;
+}