We don't need any row classes anymore because the <body> already has a
maximum width. As for columns, we only have one column in this form, so
we don't need them either. Besides, the form's parent element already
has a padding.
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.
