Move Breadcrumb and Sliderspin content to more appropriate places

Summary:
Breadcrumbs is a navigation pattern, so it should be in the Navigation Patterns section, merged with the existing page there.

Slider and Spinbox is a simple conbination of two components, so it should be another variant on the existing Slider page.

Test Plan: make html then view everything locally.

Reviewers: KDE Human Interface Guidelines, fabianr

Reviewed By: KDE Human Interface Guidelines, fabianr

Subscribers: fabianr

Differential Revision: https://phabricator.kde.org/D15342