Move older concept/exercise drafts to older-drafts folder

[colinleach]

[no important files changed]

I moved all the unmerged older learning syllabus material to older-drafts/, with subdirectories for concepts and exercises. The aim is that the Exercism website will now ignore these, even for maintainers.

No file contents were changed, only the location.

I added .gitkeep files to concepts.wip/ and exercises/concept.wip/ so they stay around, even when empty. I guess we will want to use these as a staging area for new drafts?

Comments welcome on whether this is the best way to nake the change.

I'd love to move the 3 old concepts currently in concepts/: these are going to be replaced by the new basics concept when it is merged. I'm hesitant:

• The old 3 are merged, with entries in config.sys.
• The Exercism website probably expects to find them?

Does anyone know how to deprecate a concept that is no longer needed? Exercises have a status field, but there seems to be nothing equivalent for concepts.