2.1.5: Merge pull request #268 from HSF/dev
(1) reorganize domatree functions: for order rubin jobs with event service
(2) add meta_info table, corresponding orm and core functions, corresponding alembic upgrade functions
(3) use meta_info to store min_request_id and optimize min_request_id setting (for select db partitions)
(4) fix polling event status
(5) reduce db operations
(6) fix to check whether a message has been processed