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-sounds.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'>
 	<pict type='dlog' num='16' top='6' left='6'/>
 	<text size='large' top='18' left='50' width='250' height='17'>Edit Custom Sounds:</text>
 	
@@ -81,6 +81,6 @@
 	</text>
 	<button name='left' type='left' def-key='left' top='386' left='20'/>
 	<button name='right' type='right' def-key='right' top='386' left='85'/>
-	<button name='cancel' type='regular' def-key='esc' top='386' left='405'>Cancel</button>
+	<button name='cancel' type='regular' top='386' left='405'>Cancel</button>
 	<button name='okay' type='regular' top='386' left='470'>OK</button>
 </dialog>