1. add mongo db infra.
2. add implmentation of travel requirment data access based on mongo db.
3. split the server into Devo and Prod modes, based on memory and mongo
db.
4. add service level test for both Devo and Prod modes.
5. add more ut for dao implmentations.

Signed-off-by: free-walker <wally.1981@yahoo.com>