Request for improvement of effect category functionality

[VenusGirl]

Description

Installing an add-in creates duplicate categories within the effects section.

I'd like to see them displayed as subcategories of existing categories, rather than creating duplicates.

Additional context

[cameronwhite]

I think this is something related to translations - it doesn't happen in English but I could reproduce it with another language like French

[cameronwhite]

PR #1935 fixes the issue with the duplicate submenus being added, but the remaining change is to update add-ins to use Translations.GetString("Category Name") if they're using a standard Pinta category so that the submenu names are always identical