Add doc links to Studio Designer

We need to add doc links to Studio Designer to help people starting with it.

• Layouts > Local type: https://doc.nuxeo.com/nxdoc/web-ui-document-layouts/
• Layouts > Built-in Types: https://doc.nuxeo.com/studio/working-in-view-designer/
• Layouts > Workflows: https://doc.nuxeo.com/nxdoc/web-ui-workflow-tasks/
• Layouts > Page Providers: https://doc.nuxeo.com/studio/page-providers/ or https://doc.nuxeo.com/nxdoc/web-ui-search/

• UI > Dashboard: https://doc.nuxeo.com/nxdoc/web-ui-dashboard/ (wait for easier configuration to create an how-to)
• UI > Document Pages: https://doc.nuxeo.com/nxdoc/how-to-new-pill/
• UI > Left Menu Items: https://doc.nuxeo.com/nxdoc/web-ui-search/
• UI > Main Menu Page: NEED DOC
• UI > Actions: https://doc.nuxeo.com/nxdoc/how-to-insert-user-action/
• UI > Themes: https://doc.nuxeo.com/nxdoc/web-ui-theme-customization/ (wait for easier configuration to create an how-to
• UI > Translations: https://doc.nuxeo.com/nxdoc/web-ui-managing-translations/

• Resources > https://doc.nuxeo.com/studio/left-menu/#resources-tab