Fix #6 Force save operation triggered by app entering background...

Fix #6 Force save operation triggered by app entering background to be performed on the serial queue _loggingQueue.

- Also removed initialization of NSMutableArray *logMessagesArray from the init method because that is not always triggered on the _loggingQueue

- Initializes the NSMutableArray *logMessagesArray on demand in the _loggingQueue to ensure thread safety.