Upgrade Acorn version of Foundation for Sites to 6.6.3

Acorn uses "Foundation for Sites" for its Frontend development framework. Presently, the project utilizes version 6.5. This needs to be upgrade to 6.6.3 (the most current as of this writing).

Development tasks:

• Upgrade the internal Oak-Tree version of Foundation to the upstream master.
  • Oak-Tree Internal Version: https://code.oak-tree.tech/guru-frontend/foundation.frontend
  • Foundation for Sites on GitHub: https://github.com/foundation/foundation-sites
• Update the gulp.js scripts to build and deploy the current master branch of Foundation
• Test Acorn features (frontend and back) to ensure that changes in the Foundation API have not affected the Acorn frontend code
• Fix all breakages
• Push master branch of Foundation to Oak-Tree GitLab, update Acorn submodule