Include Emoji category icons as resources too

These icons are very new in the Adwaita icon theme, so we can't
rely on them being widely available, and will just include them
for now.

gtk/Makefile.am

@@ -1320,7 +1320,7 @@ gtk.gresource.xml: Makefile.am inspector/Makefile.inc
 	  echo "    <file preprocess='xml-stripblanks'>ui/$$n</file>" >> $@; \
 	done; \
 	for s in 16x16 22x22 24x24 32x32 48x48; do \
-	  for c in actions status; do \
+	  for c in actions status categories; do \
 	    for f in $(srcdir)/icons/$$s/$$c/*.png; do \
 	      test "$$f" = "$(srcdir)/icons/$$s/$$c/*.png" && continue; \
 	      n=`basename $$f`; \