Slight refactor of message creation

Since the `getCreatedMessageData` method of the `MessageStore` is just a message specific utility, it makes more sense to put it in `ChatMessageUtils`. The debatable part here is that I then moved the call to the APIs create method to the store. The primary motivation for that was the availability of `currentThreadID`, however, this may also be more maintainable because it keeps the optimistic store update close to the server/API create call.