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/spend-xp.xml

@@ -1,6 +1,6 @@
 <?xml version='1.0' encoding='UTF-8' standalone='no'?>
 <?xml-stylesheet href="dialog.xsl" type="text/xsl"?>
-<dialog>
+<dialog escbtn='cancel'>
 	<!-- Top -->
 	<pict type='dlog' num='7' top='7' left='6'/>
 	<text size='large' top='8' left='56' width='110' height='16'>Training For:</text>
@@ -97,6 +97,6 @@
 
 	<button name='left' type='left' def-key='left' top='329' left='403'/>
 	<button name='right' type='right' def-key='right' top='329' left='470'/>
-	<button name='cancel' type='regular' def-key='esc' top='355' left='403'>Cancel</button>
+	<button name='cancel' type='regular' top='355' left='403'>Cancel</button>
 	<button name='keep' type='regular' def-key='k' top='355' left='470'>Keep</button>
 </dialog>