Shared Dateformatter for performance optimization

date formatter

+ (instancetype)uiDateFormatter
{
	static NSDateFormatter* uiDateFormatter = nil;
	static dispatch_once_t onceToken;
	dispatch_once(&onceToken, ^{
		uiDateFormatter = [[NSDateFormatter alloc] init];
		uiDateFormatter.dateStyle = NSDateFormatterFullStyle;
		uiDateFormatter.timeStyle = NSDateFormatterNoStyle;
	});
	return uiDateFormatter;
}