Update header & footer

[fharper]

What type of suggestions?

Wrong Information

What page is concerned?

No response

What version of the docs?

No response

What is the issue?

The footer blog, Slack and GitHub links need to be updated for the konstruct new ones. Same goes for the website & GitHub link in the header.

I think we could also take this opportunity to add the konstruct Twitter link in the footer.

Code of Conduct

• I agree to follow this project's Code of Conduct

[fharper]

I set it to P0, not because it's a real P0, but because the old website is still up and not showing the right information, and it's a quick fix so we don't look sloppy :)