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/forum/src/components/EditPostComposer.js

@@ -0,0 +1,64 @@
+import ComposerBody from 'flarum/components/ComposerBody';
+import icon from 'flarum/helpers/icon';
+
+/**
+ * The `EditPostComposer` component displays the composer content for editing a
+ * post. It sets the initial content to the content of the post that is being
+ * edited, and adds a header control to indicate which post is being edited.
+ *
+ * ### Props
+ *
+ * - All of the props for ComposerBody
+ * - `post`
+ */
+export default class EditComposer extends ComposerBody {
+  static initProps(props) {
+    super.initProps(props);
+
+    props.submitLabel = props.submitLabel || 'Save Changes';
+    props.confirmExit = props.confirmExit || 'You have not saved your changes. Do you wish to discard them?';
+    props.originalContent = props.originalContent || props.post.content();
+    props.user = props.user || props.post.user();
+  }
+
+  headerItems() {
+    const items = super.headerItems();
+    const post = this.props.post;
+
+    items.add('title', (
+      <h3>
+        {icon('pencil')}
+        <a href={app.route.discussion(post.discussion(), post.number())} config={m.route}>
+          Post #{post.number()} in {post.discussion().title()}
+        </a>
+      </h3>
+    ));
+
+    return items;
+  }
+
+  /**
+   * Get the data to submit to the server when the post is saved.
+   *
+   * @return {Object}
+   */
+  data() {
+    return {
+      content: this.content()
+    };
+  }
+
+  onsubmit() {
+    this.loading = true;
+
+    const data = this.data();
+
+    this.props.post.save(data).then(
+      () => {
+        app.composer.hide();
+        m.redraw();
+      },
+      () => this.loading = false
+    );
+  }
+}