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/scen-version-mismatch.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='okay'>
+<dialog defbtn='okay'>
 	<!--
 	 TODO: This dialog contains out-of-date information - the current version number, as well as how to upgrade.
 	 -->