The `use_helpers` method was added in ViewComponent 3.8.0, and it's
included by default in all components since version 3.11.0.
Note we sometimes delegated the `can?` method to the controller instead
of the helpers, for no particularly reason. We're unifying that code as
well.
Since now categories are loaded in both the investment form component
and proposal form component, and their controllers are the only
"commentable" controllers using the `@categories` instance variable, we
can remove the `load_categories` call in `CommentableActions` affecting
the create and update actions.
