Update Attestation content, add logout button

[achen2401]

Initial attestation page

• Insert NIDA graphic, remove ITHS + NCDH graphics to header.
• Streamline button flow on initial Leaf site page so that users click one button rather than three (see related PR here).
• Remove footer with manuscript citation, replace with URL directing individuals to Leaf site.

data exploration/visualization page

• Add a "Logout" button to header
• remove logout option from dropdown in header

screenshots