Leap is dead, long live leap!

[SaschaMann]

@iHiD I'd appreciate it if you could check that I did everything correctly

[ee7]

Just FYI: configlet lint will soon say something like:

The slug leap is used for both a Concept Exercise and a Practice Exercise, but must only appear once on the track: ./config.json

until there's only one leap. But it looks like this PR is handling it.

(I haven't reviewed this PR).

[iHiD]

@ErikSchierboom Could you check this PR locally pls?

[ErikSchierboom]

@SaschaMann There is a merge conflict, could you fix that?

[SaschaMann]

I'll leave it until we enable concept exercises. Otherwise it deprecates leap for no good reason.