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/TerminalPost.js

@@ -0,0 +1,29 @@
+import Component from 'flarum/Component';
+import humanTime from 'flarum/helpers/humanTime';
+import username from 'flarum/helpers/username';
+
+/**
+ * Displays information about a the first or last post in a discussion.
+ *
+ * ### Props
+ *
+ * - `discussion`
+ * - `lastPost`
+ */
+export default class TerminalPost extends Component {
+  view() {
+    const discussion = this.props.discussion;
+    const lastPost = this.props.lastPost && discussion.repliesCount();
+
+    const user = discussion[lastPost ? 'lastUser' : 'startUser']();
+    const time = discussion[lastPost ? 'lastTime' : 'startTime']();
+
+    return (
+      <span>
+        {username(user)}
+        {lastPost ? 'replied' : 'started'}
+        {humanTime(time)}
+      </span>
+    );
+  }
+}