assign escbtn and defbtn appropriately

Behaviorally: This change makes it so that Enter will never cancel
a dialog, unless that dialog only contains info to be read. Escape
will never unpredictably be treated as Enter. And some dialogs without
Escape to cancel, now can be canceled with Escape.

A lot of this just refactors dialogs to define the cancel button
at the top, not as a hotkey on a cancel button deep in the XML.
I think this makes enter/escape behavior in dialogxml files more
legible at a glance.

rsrc/dialogs/edit-item.xml

@@ -1,7 +1,7 @@
 <?xml version='1.0' encoding='UTF-8' standalone='no'?>
 <!-- NOTE: This file should be updated to use relative positioning the next time it changes. -->
 <?xml-stylesheet href="dialog.xsl" type="text/xsl"?>
-<dialog defbtn='okay'>
+<dialog defbtn='okay' escbtn='cancel'>
 	<!--
 	 TODO: Assign numeric types (type = 'int' or 'uint') to fields as appropriate
 	 -->
@@ -18,7 +18,7 @@
 	<field name='weight' top='267' left='366' width='52' height='16'/>
 	<field name='class' top='291' left='366' width='52' height='16'/>
 	<button name='okay' type='regular' top='357' left='509'>OK</button>
-	<button name='cancel' type='regular' top='357' left='434' def-key='esc'>Cancel</button>
+	<button name='cancel' type='regular' top='357' left='434'>Cancel</button>
 	<button name='prev' type='left' top='357' left='13'/>
 	<button name='next' type='right' top='357' left='76'/>
 	<!--