added an idempotent query to create potential records in trader table if it doesn't exist
make trader_id column reference/foreign key in order_event table
it helps strengthen the referential integrity of PSQL schema and adds the possibility of cascade delete on account events
later these two new transactions which were added to check if both trader and account exist in add functions can be dropped and substituted with ids creation at node startup (so we don't have to try to create them at every account or order event save)
Pull Request
tradertable if it doesn't existtrader_idcolumn reference/foreign key inorder_eventtabletraderandaccountexist in add functions can be dropped and substituted with ids creation at node startup (so we don't have to try to create them at every account or order event save)