[WIP] More permissive license

[Copilot]

• Replace the GNU GPL v3 LICENSE file with the MIT License
• Update license headers in js/Cypher.js to reflect MIT License
• Update license headers in js/GraphViewer.js to reflect MIT License
• Update license headers in index.html to reflect MIT License
• Check for any other files that might need license header updates

Fixes #45.

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