Move old `exercises/concept.wip` drafts

[colinleach]

These older drafts are causing confusion as we try to get a new learning syllabus together. They are hidden from students, but show up to maintainers in distracting and often puzzling ways.

Proposals:

• Delete the duplicate leap exercise completely (as already discussed with @depial in #784).
• Move the others to somewhere they will be ignored by the website: out of the exercises directory, to some neutral name like drafts.
• Re-use the exercise runtests.jl and example.jl as appropriate, but expect to rewrite the markdown files pretty much completely, based on reviewer feedback.
• With a bit less urgency, also move the concepts.wip directory from the top level (note the plural concepts in this case)

[depial]

It looks like I opened PR #790 around the time you were raising this issue, so I thought I'd mention it here.

I wouldn't be adverse to moving them to another location where they will be ignored so they are still around for future reference also (I saved a copy of Leap on my machine as a backup before submitting the PR just in case)

[colinleach]

I just merged #790. I'll aim to move the remaining items tomorrow.

[depial]

What are your thoughts on how to introduce learning mode material? I feel what they appear to have been doing before (staging the learning mode stuff in concepts.wip, then, once there's enough material, launching it all at once) seems reasonable.

If you think that is an okay idea, maybe we could keep the non overlapping exercises in the concepts.wip, so they aren't wiped from the site, and then work on improving or replacing them individually. I definitely liked some of the exercises in there, so I'd be happy to have a go at getting them ready.

[colinleach]

I was just thinking about this, without coming to any clear conclusions. I've been playing about with a few things (concepts more than exercises) on a private repo, intending to copy them to the main repo once I see where things might be going. It would be good to have a staging area where the two of us could discuss them before asking for a full review.

After losing 10 days to illness, I've just rewritten booleans. I'm out of time this evening, so I'll read through it again tomorrow then push the new version to #781. A power outage today didn't help - I was just getting restarted on this when everything shut down.

I'll probably do a numbers concept next, based on the Python version, so we can see where this fits into the syllabus. I'm undecided between cars-assemble or currency exchange to go with it, so that's a choice we need to make sometime.

I did a bit more work on the flowchart meanwhile, though I still need to add in some exercises we can steal from other tracks. I put together a list on Sheets with a superset of everything used on (nearly) all the syllabi, and I think there's an official list somewhere (I can't find it at the moment).

If you want to clean up some exercises, that's great. Probably best to ignore the introduction.md for now, because that can be copied from the relevant Concept once that's agreed. I worked with Bethany a bit on Python stuff, and she always leaves each introduction.md blank until everything else is finished. It tends to then be a cut-down version of about.md.

Also, I learned that Bethany is awesome, and things work better if I just do what she says.