feat: app container split

[Tahul]

Work in progress refactor of app layouts;

• Implement a default layout
• Global template state
• Handle layout from a user overridable component
• Handle toggle of UI parts per-page (aside, navigation)
• Remove unnecessary templates (avoiding boilerplate)
• Still allows layout overwriting from theme
• Allows to specify default layout from docus.config.js
• Removes full page flickering on page change

I think this is ready for review.

Known issue:

• On first render, AsideNavigation flickers once and then works well, would appreciate help on this.

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[Tahul]

Hey 😄; ready for review @bdrtsky @farnabaz @atinux

[bdrtsky]

For AppLayout.vue: I think we could wrap this slot into main tag, since it’s basically where <Nuxt/> will be rendered

Also, AppPage looks more like AppArticle, maybe rename it, since AppPage not really descriptive.

[atinux]

I like the idea of wrapping with <main>.