Use new toolbox icon for "Tools" dropdown menu button

Summary: Use the awesome new `tools` icon in the {nav Tools} dropdown menu button. Since the icon is only available in Frameworks 5.55, we use the old icon as a fallback since the minimum frameworks version is still 5.29.

Test Plan: {F6557432}

Reviewers: #spectacle, #vdg, ndavis

Reviewed By: #vdg, ndavis

Subscribers: broulik

Tags: #spectacle

Differential Revision: https://phabricator.kde.org/D18400