[backend] Hiding option values handle if object is not persisted

[backend] @option_type.option_values is always set. No need to verify it emptiness

[backend] Hiding the handle of option values if object is not persisted

Fixes #5617
Fixes #4836
Add actionable? to Promotion::Rules::Taxon

Fixes #5621
refs #4477
support callbacks on clear cache, support custom callbacks

Fixes #5623