added migrations for: link field, root item; and operation with it
added callbacks
encapsulate getting numbers and parents for new/create/edit/update into types
changed decorator and model for right conception, changed validation of number, some refactroing
changed migration filling link in standards, cause decorate.link haven't exist already
tried to modife saving links for children when link was updated
removed link from standards table, added methods link and code in model
removed method link, because it doesn't need
Merge branch 'feature/standard_model' into develop