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/components/Switch.js

@@ -0,0 +1,17 @@
+import Checkbox from 'flarum/components/Checkbox';
+
+/**
+ * The `Switch` component is a `Checkbox`, but with a switch display instead of
+ * a tick/cross one.
+ */
+export default class Switch extends Checkbox {
+  static initProps(props) {
+    super.initProps(props);
+
+    props.className += ' switch';
+  }
+
+  getDisplay() {
+    return '';
+  }
+}