Shell enhancements

Closes #95 (closed). Mid-MR, switched from GoTTY to Cockpit terminal.

Todo:

• Figure out why Elm app can talk to GoTTY status server from reactor and electron, but not in browser served from local filesystem. Mixed HTTP/HTTPS content? CORS?
  • Worst case, gracefully degrade away from using GoTTY status server
• Revise the setup_webshell.sh script to also deploy the GoTTY status server
• Ensure that GoTTY server and GoTTY status server Cockpit server survives reboots
• Remove references to GoTTY server in code, either genericize these or say cockpit instead

Wish list:

• Also expose link to Cockpit UI

For next MR:

• Somehow handle auth/login. Perhaps generate random Cockpit password and store as instance custom property? #124 (closed)
• Offer to hide cloud-init stuff from user. Perhaps give choices of either: #126 (closed)
  • 'Handle my cloud-init', sets up web terminal etc using pre-generated password
  • 'Do my own cloud-init', gives user text box for cloud config