Introduce Transaction service

[dmibod]

1. Refactor EventService to TransactionService
2. Get EventBus from Context (case 1) otherwise create new one and put in Context (case 2)
3. Fire events if (case 2), "commit" events (enqueue "compensation" events, apply events to DB)
   3.1. In case of failure, "rollback" transaction (execute "compensation" events, in case of error > log & panic)
   3.2. In case of success, fire TransactionCommitted event
4. Send notifications by TransactionCommitted event