Improve item-piechart directive

What's Changed

• item-piechart <> filtering should give priority to a missing attribute by @JasperCraeghs in #372
• Generate matrix with item-piechart directive by @JasperCraeghs in #371
• Order item-piechart slices more logically by @JasperCraeghs in #374

Full Changelog: v11.1.0...v11.2.0