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/evented.js

@@ -1,45 +1,79 @@
+/**
+ * The `evented` mixin provides methods allowing an object to trigger events,
+ * running externally registered event handlers.
+ */
 export default {
+  /**
+   * Arrays of registered event handlers, grouped by the event name.
+   *
+   * @type {Object}
+   * @protected
+   */
   handlers: null,
 
   /**
-
+   * Get all of the registered handlers for an event.
+   *
+   * @param {String} event The name of the event.
+   * @return {Array}
+   * @protected
    */
   getHandlers(event) {
     this.handlers = this.handlers || {};
-    return this.handlers[event] = this.handlers[event] || [];
+
+    this.handlers[event] = this.handlers[event] || [];
+
+    return this.handlers[event];
   },
 
   /**
-
+   * Trigger an event.
+   *
+   * @param {String} event The name of the event.
+   * @param {...*} args Arguments to pass to event handlers.
+   * @public
    */
   trigger(event, ...args) {
-    this.getHandlers(event).forEach((handler) => handler.apply(this, args));
+    this.getHandlers(event).forEach(handler => handler.apply(this, args));
   },
 
   /**
-
+   * Register an event handler.
+   *
+   * @param {String} event The name of the event.
+   * @param {function} handler The function to handle the event.
    */
   on(event, handler) {
     this.getHandlers(event).push(handler);
   },
 
   /**
-
+   * Register an event handler so that it will run only once, and then
+   * unregister itself.
+   *
+   * @param {String} event The name of the event.
+   * @param {function} handler The function to handle the event.
    */
   one(event, handler) {
-    var wrapper = function() {
+    const wrapper = function() {
       handler.apply(this, arguments);
+
       this.off(event, wrapper);
     };
+
     this.getHandlers(event).push(wrapper);
   },
 
   /**
-
+   * Unregister an event handler.
+   *
+   * @param {String} event The name of the event.
+   * @param {function} handler The function that handles the event.
    */
   off(event, handler) {
-    var handlers = this.getHandlers(event);
-    var index = handlers.indexOf(handler);
+    const handlers = this.getHandlers(event);
+    const index = handlers.indexOf(handler);
+
     if (index !== -1) {
       handlers.splice(index, 1);
     }