Add an export file name property for JasperReport

In the current implementation, ZK JasperReport exports are generated as FileInputStream and sent to the client using ZK org.zkoss.zk.au.http.AuDynaMediar. The AMedia is always generated with the file name "report."+format.

https://github.com/zkoss/zkcml/blob/master/zkex/src/org/zkoss/zkex/zul/Jasperreport.java#L565
https://github.com/zkoss/zk/blob/master/zk/src/org/zkoss/zk/au/http/AuDynaMediar.java

However, AuDynaMediar doesn't use the file name when a response is written to the client.
https://github.com/zkoss/zk/blob/master/zcommon/src/org/zkoss/util/media/AMedia.java

By adding the following, it would be possible to generate export files with a chosen file name.

1- In JasperReport, add a field for exportName (or similar).
2- In JasperReport, use the exportName + "." + format instead of "report."+format
3- In AuDynaMedia, use the media name as source name for the download if any.
for example:
if(media.getName() != null && ! media.getName().equals(""))

{ response.setHeader("Content-disposition","inline; filename="+media.getName() ); }