Add comments for TODO

Yep/AppDelegate.swift

@@ -312,13 +312,16 @@ class AppDelegate: UIResponder, UIApplicationDelegate {
     }
 
     func sync() {
-
+        
+        // TODO 随着群组和好友越来越多，这个方法会导致 App 开启的时候，获取到离线消息愈来越慢
+        
         syncFriendshipsAndDoFurtherAction {
             syncGroupsAndDoFurtherAction { [weak self] in
                 self?.syncUnreadMessages() {}
             }
         }
 
+
         officialMessages { messagesCount in
             println("new officialMessages count: \(messagesCount)")
         }

Yep/Services/YepServiceSync.swift

@@ -957,6 +957,8 @@ func syncMessageWithMessageInfo(messageInfo: JSONDictionary, messageAge: Message
                         let newUser = User()
 
                         newUser.userID = senderID
+                        
+                        //TODO 服务器个消息的 Sender 加入一个用户状态，避免暴力标记为 Stranger
 
                         newUser.friendState = UserFriendState.Stranger.rawValue
 
@@ -980,6 +982,7 @@ func syncMessageWithMessageInfo(messageInfo: JSONDictionary, messageAge: Message
                         var sendFromGroup: Group? = nil
 
                         if let recipientType = messageInfo["recipient_type"] as? String {
+
                             if recipientType == "Circle" {
                                 if let groupID = messageInfo["recipient_id"] as? String {
                                     sendFromGroup = groupWithGroupID(groupID, inRealm: realm)
@@ -1001,6 +1004,8 @@ func syncMessageWithMessageInfo(messageInfo: JSONDictionary, messageAge: Message
 
                                         sendFromGroup = newGroup
                                         
+                                        // TODO 存在多次网络查询这个 Group 的可能性
+                                        
                                         groupWithGroupID(groupID: groupID, failureHandler: nil, completion: { (groupInfo) -> Void in
                                             dispatch_async(realmQueue) {
                                                 guard let realmForGroup = try? Realm() else {