Revise the whole terminology one more time#19

I still don't like e.g. `GENA_USE_SAMPLE`, `GENA_USE_ENTITY` and so on, as they're not intuitive. The new approach to defining a terminology should be next: - avoid homonyms; - prepare an initial list of words that can be used, then select from them by considering intuitivity; - ... (I'll think about it later, now I'm slightly discouraged).