Cruise control lessons missing

[yabberyabber]

I think the cruise control lesson might have gone missing. I see the source code is still present https://github.com/janismac/ControlChallenges/blob/gh-pages/js/levels/CruiseControl2.js

but I don't see it in the "Select a Level menu"

I think the issue is that it's just forgotten in this list of LEvelGroups here https://github.com/janismac/ControlChallenges/blob/gh-pages/js/ui.js#L136 --- it seems like we just need to add a little chunk in like this

CC.levelGroups.CruiseControl = {
  Intro: "Intro",
  Level2: "Level 2",
}

I use this tool every year to help students learn the basics of control theory and it has been very useful. The cruise control lesson has been particularly useful when talking about the difference between position control and velocity control. Thank you so much for posting and maintaining it.