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_test.go

@@ -1247,6 +1247,7 @@ func TestUserUpdateNotify(t *testing.T) {
 	data["email"] = "true"
 	data["desktop"] = "all"
 	data["desktop_sound"] = "false"
+	data["comments"] = "any"
 
 	if _, err := Client.UpdateUserNotify(data); err == nil {
 		t.Fatal("Should have errored - not logged in")
@@ -1267,6 +1268,9 @@ func TestUserUpdateNotify(t *testing.T) {
 		if result.Data.(*model.User).NotifyProps["email"] != data["email"] {
 			t.Fatal("NotifyProps did not update properly - email")
 		}
+		if result.Data.(*model.User).NotifyProps["comments"] != data["comments"] {
+			t.Fatal("NotifyProps did not update properly - comments")
+		}
 	}
 
 	if _, err := Client.UpdateUserNotify(nil); err == nil {
@@ -1300,6 +1304,12 @@ func TestUserUpdateNotify(t *testing.T) {
 	if _, err := Client.UpdateUserNotify(data); err == nil {
 		t.Fatal("Should have errored - empty email")
 	}
+
+	data["email"] = "true"
+	data["comments"] = ""
+	if _, err := Client.UpdateUserNotify(data); err == nil {
+		t.Fatal("Should have errored - empty comments")
+	}
 }
 
 func TestFuzzyUserCreate(t *testing.T) {