Request: Add new social icon in the sidebar: XMPP/Jabber, Matrix, tildes

[silverhook]

I haven’t found a good one yet, but this is how Jabber looks like (too wide for our use): https://commons.wikimedia.org/wiki/File:Jabber_logo.svg

And here is the Matrix official logo (also to wide, I know): https://github.com/matrix-org/matrix.org/blob/master/gatsby/static/images/matrix-logo.svg

Tildes’ logo is also just in PNG, but we can probably get away with any tilde in a square: https://gitlab.com/tildes/tildes/-/blob/master/tildes/static/images/tildes-logo-144x144.png

[silverhook]

I found a nice Matrix icon at the bottom of this website, but no idea how to grab it: https://planet.kde.org/