rearrange support n numbers, downloader.js fixes

src/main/resources/templates/pdf-organizer.html

@@ -31,7 +31,7 @@
 						    </div>
                             <div class="form-group">
                                 <label for="pageOrder" th:text="#{pageOrderPrompt}"></label> 
-                                <input type="text" class="form-control" id="pageOrder" name="pageOrder" placeholder="(e.g. 1,3,2 or 4-8,2,10-12)" required>
+                                <input type="text" class="form-control" id="pageOrder" name="pageOrder" placeholder="(e.g. 1,3,2 or 4-8,2,10-12 or 2n-1)" required>
                             </div>
                             
                             <button type="submit" id="submitBtn" class="btn btn-primary" th:text="#{pdfOrganiser.submit}"></button>