create deprecation banner on all pages

[lauriemerrell]

Description

This PR adds a banner notifying visitors that the site is no longer being updated and directing them to the data analysis README for raw data access.

Checklist

• I am requesting to merge into the dev branch
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

Screenshots

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