MenuSorter: initial implementation

* Menus are now sanely configurable
* Custom separator placement for clearer menus

frontend/apps/reader/modules/readerbookmark.lua

@@ -45,12 +45,12 @@ end
 
 function ReaderBookmark:addToMainMenu(tab_item_table)
     -- insert table to main reader menu
-    table.insert(tab_item_table.navi, {
+    self.ui.menu.menu_items["bookmarks"] = {
         text = self.bm_menu_title,
         callback = function()
             self:onShowBookmark()
         end,
-    })
+    }
 end
 
 function ReaderBookmark:isBookmarkInTimeOrder(a, b)