suggestion: consolidate some links #122

The links on the right have become very numerous. I would suggest these changes:

(1) Replace Mastodon, Chat, Discord, Telegram, Instagram with a single link called "Socials". Create a new page /socials. Include these links there.

(2) Now we have three links to pads, but in practice only the "Stammtisch Pad" is in use. I would suggest removing the other two for now; I feel they might be more distracting than useful for visitors.