Make a staggered second row of preset icons in the popup palette for large values.

Summary:
30~ presets in the popup palette current leads to very tiny icons.

This patch adds the ability for a second row of presets to be added, so the icons won't have to be as tiny.

30 preset slots.

21 preset slots.

Reviewers: Krita, dkazakov

Reviewed By: Krita, dkazakov

Subscribers: dkazakov, scottpetrovic, Krita

Tags: Krita

Differential Revision: https://phabricator.kde.org/D19597