Fix translations of $GenericName

Summary:
$GenericName was translated before being passed to KMoreToolsService::formatString,
causing translators to process "$GenericName - ..." in their language, in turn causing formatString not to replace the expected placeholder.

Test Plan:
In another language than English:
Open Dolphin
Click on the free space progress bar
Menu appears

Before (with French) :
First entry begins with "$NomGénérique -..."

After:
First entry begins with "Statistiques d'utilisation des disques - ..."

Reviewers: leinir, ngraham, Localization, aspotashev

Reviewed By: ngraham, aspotashev

Subscribers: aspotashev, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D25216