Provide a way to set a preffered filename for a contentitem

[Dan Chapman ]

If an application uses QTemporaryFile to store a file to export through content-hub the exported filename contains the XXXXXX template portion of the temp file name. Which can make finding the exported file in the destination application challenging due to the funky file names. i.e holiday.pdf.XXXXXX or my-app-XXXXXX_holiday.pdf

It would be great to be able to set a "preferred" filename on the ContentItem object that would get used at the receiving end of the content share.

This is an issue I've just come across in Dekko (bug 1522984) but I think it applies to any app that uses temporary files for sharing content.