Use a better way to generate a favicon

[flovan]

The current way of generating a favicon for legacy browsers isn't actually producing a valid file (renaming a .png to .ico, what was I thinking!).
Try finding something like Node favicon-generator, but, if possible, without imagemagick.

[flovan]

Not a fan of the added dependencies, so abandoning this for now.

[flovan]

Now using real-favicon, which was added in a5e70d7.

Keeping this issue open until https://github.com/RealFaviconGenerator/real-favicon/pull/2 is merged OR the module aligns with the latest (stable) API.

[flovan]

@CREEATION Email never forgets 😉

The maintainers contacted me by email to let me know that the API was going to undergo some changes which would make the PR redundant. I might revisit this feature at some point, or I might not, as it adds quite a lot of bloat to the build process.

Thanks anyway for keeping an eye out!