Don't hardcode fa-plus <https://github.com/NodeBB/NodeBB/pull/5050#issuecomment-256862345>

templates/partials/topic/post.tpl

@@ -86,7 +86,9 @@
 	<!-- IF posts.replies -->
 	<br />
 	<a component="post/reply-count" href="#" class="no-select">
-		<i class="fa fa-plus"></i>
+		<i class="fa fa-plus" component="post/replies/open"></i>
+		<i class="fa fa-minus hidden" component="post/replies/close"></i>
+		<i class="fa fa-spin fa-spinner hidden" component="post/replies/loading"></i>
 		[[topic:replies_to_this_post, {posts.replies}]]
 	</a>
 	<!-- ENDIF posts.replies -->