Filter parts by 'is_assembly'

Also greatly improve rendering of the Part table

InvenTree/templates/table_filters.html

@@ -80,7 +80,11 @@ function getAvailableTableFilters(tableKey) {
             low_stock: {
                 type: 'bool',
                 title: '{% trans "Low stock" %}',
-            }
+            },
+            assembly: {
+                type: 'bool',
+                title: '{% trans "Assembly" %}',
+            },
         };
     }