org-odt.el: Add default character style

* lisp/org-odt.el (org-export-odt-default-org-styles-alist):
Add default character style.

lisp/org-odt.el

@@ -380,7 +380,8 @@ This variable is effective only if
 		  (table . "Table")
 		  (definition-term . "Text_20_body_20_bold")
 		  (horizontal-line . "Horizontal_20_Line")))
-    (character . ((bold . "Bold")
+    (character . ((default . "Default")
+		  (bold . "Bold")
 		  (emphasis . "Emphasis")
 		  (code . "OrgCode")
 		  (verbatim . "OrgCode")