LPS-31462 Messaging infrastructure

Hey Mike,

I've found some more stuff to fix in the messaging infrastructure and I've did the changes.

Also as we had the discussion that @zberentey already added the code for counting the entities during export and import. I think that it is not necessary to count the entities through the messaging, but I've moved Zsolt's code to the SMDHInvocationHandler. The reason is that we had a discussion that there might be advices for the data handlers, and I'd like to collect these kind of operations (what are not strictly tied to the data handlers themselves) to the invocation handlers to see if there is need for multiple advices or an invocation handler is enough, etc.

Thanks,

Máté