Add breadcrumb stub

[obulat]

Fixes

Fixes #214 by @panchovm

Description

This PR adds the breadcrumb stub. It will be replaced by a Vocabulary Vue component when it is available. Also, when the structure of the site and parent pages is clear, we will need to update them, too.

Screenshots

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
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• My code follows the established code style of the repository.
• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

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