Prevent duplicate commits

[skofman1]

When can duplicate commit happen?
Two commit requests are sent concurrently, and two requests end up in the Topic, before the DB is updated to prevent further commits.

Solutions:

1. Locking on commit method
2. Service bus duplicate detection:
   http://blog.iquestgroup.com/en/windows-azure-service-bus-duplicate-detection/#.Vw7R1DArJaR
   Use a hash to distinguish between different commits, and recognize the same commit. For example, request time stamp of previous commit.