Dev 9, Windows and Windows XP themes are the same

[ja231c]

They looked noteably different in Dev 8.

[hexabits]

I think this is due to a change between Qt 5.x (dev 8) and Qt 5.15 (dev 9), where it now requires qwindowsvistastyle.dll in styles folder.

I forgot to copy the styles folder to the release folder for this release.

Unfortunately I tried with the plugin and now both Windows/Windows XP look like Windows. Without the plugin both Windows/Windows XP look like Windows XP. I will have to look into what else changed in Qt 5.15 regarding styles.