Fixed #111: Drop::sendAndForget can return a false value

Add new classes DropResultContact and DropResult 
Fixed #111: Drop::sendAndForget can return a false value

Close #195 
Normally one ot this both function is enough. But when you look into DropResult::addContactResult. This function does not check the complete list only the state. DropResultContact can also use for other cases. My prefered name was NetworkMessageSendingResult and NetworkMessageSendingResultContact.