Batch size configuration option should only affect display batch size ("it" value)

The former 'batchSize' configuration option we provided to users (config.set('batchSize', ...) and config.get('batchSize')) is now called 'displayBatchSize' as it will only affect the number of results displayed for a cursor. This is also the property to be used instead of DBQuery.shellBatchSize that was available in the old shell.