Refactoring based on new/correct eslint and prettier config, proxmox lxc provider

Admin page and course management, refactoring

updated reat-router and mermaid, added notistack, ensure proper pruning of instances ssh conns, support lsp conn over jumphost, support multiple logins from same user (introduced sessions), fix ff websocket lag, fix terminal garbage control seq in xterm.js, ensure proper proxmox id/ip and node failure handling, support for individual JWT tokens

Update README.md

fix: tolerate proxmox hosts being down also during deletion of instances