All dialogs now use default skin and foreground colour

(The attributes are still available in the schema though, and will not be removed.)

rsrc/dialogs/quit-confirm-save.xml

@@ -1,6 +1,6 @@
 <?xml version='1.0' encoding='UTF-8' standalone='no'?>
 <?xml-stylesheet href="dialog.xsl" type="text/xsl"?>
-<dialog skin='dark' defbtn='save'>
+<dialog defbtn='save'>
 	<pict type='dlog' num='23' top='9' left='9'/>
 	<text size='large' top='5' left='52' width='254' height='18'>Do you want to save before quitting?</text>
 	<button name='save' type='large' top='31' left='230'>Save First</button>