[server][ItemGroupStream] Add a new class: ItemGroupStream.
[server][ItemGroupStream] Add a new operator:  uint64_t &operator<<(uint64_t &lhs, ItemGroupStream &igStream).
[server][testItemGroupStream] Clean up.
[server][ItemGroupStream] Add a new operator: string &operator<<(string &lhs, ItemGroupStream &igStream).
[server][DBClientUser] Clean up (improve readability with ItemGroupStream).
[server][ItemGroupStream] Add a new method: getItem().
[server][DBClientAction] Clean up by replacing DEFINE_AND_ASSERT() with GroupItemStream.
[server][ItemGroupStream] Clean up.
[server][DBClientAction] Clean up by replacing GET_*_FROM_GRP() macro with GroupItemStream.
[server][ItemGroupStream] Add a comment.
[server][ItemGroupStream] Add a new method: CAST_TYPE pull(void).
[server][DBClientUser] Clean up by replacing GET_*_FROM_GRP() macro with GroupItemStream.
[server][ItemGroupStream] Overload a new operator: >>(int &).
[server][testItemGroupStream] Clean up.
[server][testItemGroupStream] Use a camel case.
[server][ItemGroupStream] Overload an operator: >>(uint64_t &).
[server][ItemGroupStream] Overload an operator: >>(string &).
[server][DBClientUser] Use '>>' instead of '<<'.

With this way, it is easy to adjust the position of variables.
[server][DBClientAction] Replace '<<' with '>>' to improve simplicity.
[server][DBClientConfig] Replace '<<' with '>>' to improve simplicity.