Enable KDE localization and icon integration in Grantlee

Summary:
This allows us to do i18n calls in the templates rather than having to
export whatever we need as property, as well as look up icons directly
from the templates.

Reviewers: mlaurent

Reviewed By: mlaurent

Subscribers: kde-pim

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D20717