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/basic-portal.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='no'>
+<dialog defbtn='no'>
 	<button name='no' type='regular' def-key='n' top='39' left='244'>No</button>
 	<button name='yes' type='regular' def-key='y' top='39' left='178'>Yes</button>
 	<pict type='dlog' num='22' top='9' left='9'/>