PLT-914 Add mention notifications for replies on a comment thread (#3130)

* PLT-914 Add mention notifications for replies on a comment thread

* remove useless store method
fix highlighting comments posted before th user write something to thread

* refactor out isCommentMention function after rebase

* change comment bar highlighting to replay icon mention highlighting

* settings and always visible highlight

* fix unit tests for new settings

* change highlight behaviour
- if any message in comment thread generates mention - all thread is highlighted
- remove always visible highlightion

* fix bug about the textarea in the center channel not clearing

* fix default settings value notify_props.comments

* do not highlight own comments if there is no other user's messages in thread

* refactor out ReactDOM.findDOMNode

* refactor out using of UserStore from component

api/user.go

@@ -1930,6 +1930,12 @@ func updateUserNotify(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	comments := props["comments"]
+	if len(comments) == 0 {
+		c.SetInvalidParam("updateUserNotify", "comments")
+		return
+	}
+
 	var user *model.User
 	if result := <-uchan; result.Err != nil {
 		c.Err = result.Err