Add option to prepend heading to content before first (sub)heading

Like this, when exactly one field is missing and there is content
before the first (sub)heading, the heading is seen as part of that
content and one can avoid having to duplicate it there. The
content with the prepended heading will be mapped to the missing
field. Notes in Anki and Org can be made to look more similar
without always needing a separate field for the heading.

anki-editor.el

@@ -123,6 +123,12 @@ For example, you can put custom styles or scripts in this variable."
 A leading logical operator like `+' or `&' is required."
   :type 'string)
 
+(defcustom anki-editor-prepend-note-heading nil
+  "Prepend note heading to contents before first (sub)heading.
+This is only in effect when exactly one note-type field is not found
+among the note subheadings and there is content before the first subheading."
+  :type 'boolean)
+
 
 ;;; AnkiConnect
 
@@ -776,18 +782,33 @@ Return a list of cons of (FIELD-NAME . FIELD-CONTENT)."
 		 (if (equal "" (string-trim content-before-subheading))
 		     (push (cons (car fields-missing) heading)
 			   fields)
-		   (push (cons (car fields-missing) content-before-subheading)
+		   (if anki-editor-prepend-note-heading
-			 fields))
+		       (push (cons (car fields-missing)
+				   (concat heading "\n\n"
+					   content-before-subheading))
+			     fields)
+		     (push (cons (car fields-missing)
+				 content-before-subheading)
+			   fields)))
 	       (if (equal "" (string-trim content-before-subheading))
 		   (push (cons (car fields-missing)
 			       (anki-editor--concat-fields
 				fields-extra subheading-fields level))
 			 fields)
+		 (if anki-editor-prepend-note-heading
+		     (push (cons (car fields-missing)
+				 (concat heading "\n\n"
+					 content-before-subheading
+					 (anki-editor--concat-fields
+					  fields-extra subheading-fields
+					  level)))
+			   fields)
 		   (push (cons (car fields-missing)
 			       (concat content-before-subheading
 				       (anki-editor--concat-fields
-				      fields-extra subheading-fields level)))
+					fields-extra subheading-fields
-		       fields))))
+					level)))
+			 fields)))))
 	    ((equal 2 (length fields-missing))
 	     (if (equal 0 (length fields-extra))
 		 (progn