Feature: Add duplex sort / collate tool

tools.html

@@ -673,6 +673,12 @@
           category: 'merge-split',
           icon: 'shuffle',
         },
+        {
+          name: 'duplex-collate',
+          title: 'Duplex Collate',
+          category: 'merge-split',
+          icon: 'arrows-vertical',
+        },
         {
           name: 'combine-single-page',
           title: 'Combine Pages',