Extend categories

[LisiLisenok]

1. Add more categories, now only SDK is available. Possible categories: test, serialization, collection, io, etc.
2. Any published module has to belong to at least a one category.
3. Module which starts from 'herd' must include category name also, like herd.'category'.
4. User may suggest category to be reviewed and added by administrator.
5. Category may have some brief description.