[effects] Move Fall Apart and Sheet to the Candy category

Summary:
The Fall Apart effect and the Sheet effect look like "candies" so
let's move them to corresponding category.

Test Plan:

Reviewers: KWin, Plasma, VDG, ngraham, davidedmundson

Reviewed By: KWin, Plasma, VDG, ngraham, davidedmundson

Subscribers: ngraham, kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D14517