use underscores during rename and move

data/interfaces/default/config.html

@@ -498,6 +498,9 @@
                                 <input type="text" name="file_format" value="${config['file_format']}" size="43">
                                 <small>Use: $Disc/$disc (disc #), $Track/$track (track #), $Title/$title, $Artist/$artist, $Album/$album and $Year/$year</small>
                             </div>
+                            <div class="checkbox row clearfix">
+                                <input type="checkbox" name="file_underscores" id="file_underscores" value="1" ${config['file_underscores']}/><label>Use underscores instead of spaces</label>
+                            </div>
                         </fieldset>
 
                         <fieldset>