Display count badges in sidenav tree

Uses the 'tags' parameter as according to the docs - https://github.com/jonmiles/bootstrap-treeview

- Part
- Stock

InvenTree/part/models.py

@@ -47,18 +47,17 @@ class PartCategory(InvenTreeTree):
         verbose_name = "Part Category"
         verbose_name_plural = "Part Categories"
 
+    @property
+    def item_count(self):
+        return self.partcount
+
     @property
     def partcount(self):
         """ Return the total part count under this category
         (including children of child categories)
         """
 
-        count = self.parts.count()
-
-        for child in self.children.all():
-            count += child.partcount
-
-        return count
+        return len(Part.objects.filter(category__in=self.getUniqueChildren()))
 
     @property
     def has_parts(self):