Implement more CQRS oriented structures

[osoykan]

• Command, SequencedCommand

• CorrelationId/CausationId approach for each command

• CorrelationId/CausationId aware Context implementation. This will provide these Ids in its context
  e.g ICommandContext {CorrelationId, CausationId} per thread.

  Enter context (command)
  Do stuff
  Save
  

• Consider removing ApplicationServices and introduce CommandHandler and provide a generic IHandles<T>

[osoykan]

Think about MediatR as a core library to handling commands (?)