Tweak default icewm preferences

Attention: this patch is applied in the %build phase, because it patches
a file generated by ./src/genpref. To edit the patch:

  quilt setup icewm.spec
  cd icewm-<version>
  quilt push -a
  ./configure <options from the spec>
  make -C src genpref
  ./src/genpref >src/preferences
  quilt import -p0 patches/icewm-preferences.patch
  quilt push
  vi lib/preferences
  quilt refresh
---
 src/preferences |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

Index: src/preferences
===================================================================
--- a/src/preferences
+++ b/src/preferences
@@ -542,7 +542,7 @@
 # NetWorkAreaBehaviour=0 # [0-2]
 
 #  Icon search path (colon separated)
-# IconPath="/usr/share/icons/hicolor:/usr/share/icons:/usr/share/pixmaps"
+IconPath="/usr/share/icons/Adwaita/16x16/apps:/usr/share/icons/hicolor:/usr/share/icons:/usr/share/pixmaps"
 
 #  Mailbox path (use $MAIL instead)
 # MailBoxPath=""