README: Improve links and intro

A slight reword of the intro, and a navigation bar above the intro to
quickly jump to the client repo or PS main.
Make sure that alts leave when a user is banned from a room
If a user is renamed, check if they are banned from their current rooms
Merge pull request #1021 from Slayer95/roomban

Fixes for room bans
Merge pull request #36 from Zarel/master

Patch 36