Use macro %{_desktopdir} instead of %{_datadir}/applications.
Use macro %{_iconscaldir} instead of %{_datadir}/icons/highcolor/scalable.
Use macro %{_iconbasedir} instead of %{_datadir}/icons/highcolor.
Fix path for man-page.
Call gtk-update-icon-cache in post-install-scriptlet, too.

Not only in post-uninistall and post-trans.