Implement localisation

[Mrtenz]

Since #308 was done, we now have different language files, but these were not actually used yet, other than the English file. In this pull request I've added actual support for localisation.

• I had to swap out the Gatsby Head API for React Helmet, since the Head API is not wrapped in the page context and does not have access to the locale data. This is a known issue in Gatsby, and the maintainers recommend using Helmet.
• I've moved most of the stuff in the different Head components to a shared SEO component.

Todo

• [x] Right now all pages are deleted. We need to make sure the 404 page isn't deleted.
• [x] Redirect based on the browser locale.

Closes #314.

[github-actions[bot]]

Commit 0aa117746ec3fa4bcd21cacf49c544ca02c006e0 successfully pushed to staging website:

https://metamask.github.io/snaps-directory-staging/pr/328/

[socket-security[bot]]

New and removed dependencies detected. Learn more about Socket for GitHub ↗︎

Package	New capabilities	Transitives	Size	Publisher
npm/gatsby-plugin-react-helmet-async@1.2.3	Transitive: environment, eval, filesystem, network, shell, unsafe	+1382	471 MB	me4502
npm/react-helmet-async@2.0.4	Transitive: environment	+8	5.05 MB	wonderboymusic
npm/shallowequal@1.1.0	None	0	7.35 kB	dashed

🚮 Removed packages: npm/arch@2.2.0, npm/babel-plugin-lodash@3.3.4, npm/nice-try@1.0.5, npm/p-finally@1.0.0, npm/strip-eof@1.0.0

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