Added the old Twitter logo; added myself to the list of users

[kompoth]

While there is no such social network as Twitter now, I and some people I know still prefer to use the word 'Twitter' when mentioning X. I also personally like the old branding more. Adding it to the list of available SVGs wasn't a big deal, so here it is.

I also took the liberty to add my brand new web page to the list of this awesome theme users :)

[tomfran]

Nice thanks for the PR, could you please include a screenshot with a bunch of other icons to see it it matches the overall style?

[kompoth]

Yeap, sure!

I took this SVG from Wikimedia, adjusted it in the Inkscape and just copy-pasted the resulting path to the layouts/partials/svg.html.

Here is a working example: https://kmiziz.xyz/

UPD: just figured out that the current path differs a bit from the ones on the screenshots as I have fixed the vertical alignment after making those screenshots.