Expert: attributes streaming definition for indexing facets
Steaming of facets attributes is a low level indexing interface with Lucene indexing.
There are two types of category related streams:
  - Category tokenizer stream handles tokenization for a single category, 
  e.g. for creating drill-down tokens.
- Category list tokenizer stream handles tokenization for multiple categories, 
  e.g. for creating a counting list token, representing all the categories of 
  a certain document.