Fix minor UI and content inconsistencies on DeepChem.io

[Nesar976]

This PR addresses a set of small UI and content consistency issues reported in Issue #50.

Summary of changes:

• Updated footer content (copyright year and social label).
• Fixed inconsistent carousel navigation behavior on the homepage and About page.
• Removed the “Back to Top” button from the Tutorials section to maintain consistent behavior across the site.
• Updated the website logo to match the current DeepChem GitHub repository branding.

All changes are intentionally minimal and scoped to avoid any layout or design changes.
Please let me know if you’d like any part of this split differently or adjusted further.