Update social links

[tillywoodfield]

Code changes:

• Commit the icons as svg files to make the code more readable, as vite automatically inlines them when the css is built, so it's unnecessary to have it in the code

Visual changes:

• Add link to the IATI Facebook account
• Replace the Twitter logo with the X logo
• Update the usage of each social brand's logo to be inline with their guidance (remove the extra white background from each logo, use the white versions on the dark background, and add more space between each icon)

Closes #19

[tillywoodfield]

@robredpath are you okay with this change from a visual perspective?

[github-actions]

🎉 This PR is included in version 3.0.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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