Categories

Origin	flow/engineering/engineering.yml 119:5
Uri	engineering://nasdanika/modules/core/modules/flow/issues/categories
Target	Flow
Workable

Grouping mechanism, maybe have it in Ncore. A category is a named element with id (use uuid?). Elements have a list of categories. If it is not empty, elements may be grouped into categories with categories list being a (tree) path. Can be used to group service activities into "domains". Categorization does not affect URI's.