Link to Qt version changes documentation in online installer

On the Interest mailing list, Sean Murphy said:

Thanks for the link! I had never stumbled across the "Changes to <Qt Module Name>" sections of the docs, so now I've got a whole bunch of new reading to do!

Most users would likely be in the same boat if they don't know to look for these pages in the documentation, so it could be worthwhile to include a link to the changes documentation in the installer. For example, we could put it at the top of the progress dialog while the packages are downloading so they can read it while they wait. For minor versions we could provide a link to the change log.

If there would be too many links when the user is downloading several Qt versions, maybe we could just do it for major versions.