[Enhancement]: Improve the handle situations of being unable to receive messages either by carrier network or by dstore.

[SquareTools]

can't receive the offline messages, the steps are:

1. A and B are friends
2. A and B are all online
3. when the app exits at B, then A sends messages to B before receiving the DisConnect state
4. when the app starts at B, B can't receive the messages from A.

[stiartsly]

Quoted from wechat group of Elastos Carrier Internatnl Devs listed by @peter-strauss:

1. "@stiartsly we have found two new situations that may need improvement:"
2. "1st situation: user1 is online, user2 connects to the carrier network, but does not see user1 online yet (short period of time) -> user2 sends user1 a message -> message is sent to dstore, although user1 is actually online -> user1 does not receive the message until carrier is restarted";
3. "2nd situation: user1 and user2 are both online -> user1 goes offline, but user2 sees user1 still as online (short period of time) -> user2 sends user1 a message -> message is not stored on dstore, nor received by user1 -> message is lost"