update section cv mapping to item[subject] [BOR-28]

[devketanpro]

No description provided.

[IvanJelicSF]

Thanks @devketanpro, I guess things like sections_cv_items = self.get_cv_items("categories") and voc_categories = self.get_cv_items("sections") have only semantic implications as we are using sections_cv_items for categories and voc_categories for sections :)

[devketanpro]

my bad, I forgot to update the variable name.
categories CV we used to populate the default category, and section CV used for section field, which is populated under the item['subject']