Async support

[mlidbom]

The event store, document database, message handler interfaces should all have async versions of the appropriate methods

[mlidbom]

When we do this, check out: https://github.com/BigBabay/AsyncConverter it might be very helpful.

[mlidbom]

This is an ongoing effort. Most of the hypermedia parts already fully supports async and the endpoint setup etc is all async.