Category and Content improvements

• As a developer I would like to have different domain model for Categories and Content so that some operations can be simplified in code.
• I would like to optimise content hierarchy so that searches could be performed reliably within scope of a shop.
• I would like to improve performance of checks to determine if category/content belongs to shop

In addition to the above there was an idea to standardise the approach to content includes.

Currently to have placeholders in theme we use shop code prefix strategy in the URI and it is a bit of nuisance to prefix every content include. Therefore an ice is put forward to add shop code field as property on the Content object after refactoring. This could be repopulated with the shop code at the point of content creation. Then the URI resolver could be modified to search in two fields rather than concatenating. This would also require some rework on content URI caching and resolution.

Expanding this idea further in YCE we could create fallback in content service so allow per subshop override of the templates, with fallback on master shop content.

Lastly we need to refactor the content body attributes into fully fleshed CLOB.