move batcheventprocessor test into subnamespace
fix eventhandler interface
update batcheventprocessor tests to use countdownlatch and internal result object
refactor the test suite structure
move pthreads tests to subnamespaces
update batcheventprocessortest and test assets
refactor AggregateEventHandlerTest
update AggregateEventHandlerTest and BatchEventProcessorTest

move testassets to subnamespaces, too