* Feature: allow examples of variants

Adds technical support to facilitate #1530 by:

1. Adding a new component cotnext variable `isExample: true`
2. Adding template support in the component library

While these are technically new variants, they do not generate additional template files and are shown in contextually appropriate way.

Incroporating examples also brings some required updates to the layout of  the component pages — most of which have been overdue, such as removing the tree layout (whose function is planned to be replaced by the forthcoming mega menu).