Change X11 Window WM_CLASS to 'dosbox-staging' to avoid conflicts with
upstream DOSBox, which might be provided by package manager.
Update .desktop file to specify WMClass to be correlated with
dosbox-staging process (even if executable file conflicts with dosbox
upstream).
Update contrib/icons/Makefile to generate 'hicolor' directory structure.
Remove pre-rendered icons, we don't need them any more. Vector designs
for small icons are grouped in small-svg directory - these are slightly
less detailed and adjusted to render more clearly in specific sizes.
macOS utilities for creating .icns file are non-deterministic and
the resulting file has different checksum each time the file is
re-generated. We don't want this to influence reproducibility of
builds in the future.
Windows is missing necessary native utilities for generating .ico
files out of .png sources.
It's also easier to just copy generated file during snapshot build.
SVG icon as a source for other sizes, PNG icon 1024x1024 as source for
generating .icns file, and small 16x16 PNG icon.
Background circle uses size and colours recommended by Gnome HIG.
