Make category item template cache to theme-specific

In 5.2.0 version of In-Portal memory caching is enabled by default and I've spotted some interesting bug.

When you:
1. have multiple themes enabled
2. #in-commerce/item_design key in theme.xml file has different value in each theme

Then you'll get category page displayed instead of item detail page when viewing 1 of these 2 themes (which one depends on which theme was used during initial cache building).