Update MUI to v5

[Zenoo]

This PR should update the template to use MUI v5.

[vercel]

@Zenoo is attempting to deploy a commit to the RMUIF Team on Vercel.

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[vercel]

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🔍 Inspect: https://vercel.com/rmuif/web/H9YwS7wYskJeKZiZ2m7C3t8fSbJZ
✅ Preview: Failed

[Zenoo]

The Vercel build seems to fail because it's using an outdated version of Node (12).
CRA dropped support for Node 10 and 12 in 5.0.0.

[phoqe]

Hello @Zenoo! Thank you for making this PR. It was a long overdue from my part. I see there's a build error and I don't have time to look at it just now. Will return.

[Zenoo]

No problem @phoqe. The error should be fixed if you upgrade the Node version used by Vercel.