Changes

adwaita-icon-theme 3.28.0
This is the default GNOME 3 icon theme. Packaging it because I am used 
to it. When used in MATE one or two additional items (on top of Nimbus) 
in Applications and System menu are with default icon, otherwise looks 
reasonable.
To build this we need /usr/bin/gtk-encode-symbolic-svg from GTK3 package 
and perhaps other utilities. So we could require just GTK3 package but 
Win32 build documentation suggest GDK Pixbuf is needed
(https://github.com/GNOME/adwaita-icon-theme/blob/ac0826d3fc37779d64a8f3691c89914301d9ad86/win32/adwaita-msvc.mak.in#L146). 
So I pick this one instead.
 (commit: 1e76474)