Resolve #3485622 "Update legacy themes"

Some notes on the code changes:

1. I don't think I'm passing along the correct state (pending/passed/failed) to the lessons. Could use some help with that.
2. I'm not sure if my approach to having the items be links vs not is the best one.
3. Using the template files, we previously had the ability to add additional markup to each item, like an <i> or <span> tag to help indicate status. Is there a good way to do that using render arrays? Or should I just leave that up to future themers who do overrides? I'm leaning toward the latter but am curious if there's an obvious solution.
4. I feel like a lot of the code in StepsBlock.php could be refined, but not sure if this is the best time to do it so I didn't do much other than what I needed to, I think.
5. I think "locked" means we shouldn't be able to navigate to that item, but I don't think I'm defining it correctly because it's still showing up as a link even when I shouldn't be able to navigate to it. I have an if statement in place for lesson links, but not activity links and I need help getting this (be a link if not locked) to work.
6. I put the container theme suggestion in with OtherHooks and tried to modify it to match the new format, but I must be missing something because it's not picking up on the new theme suggestion.