Change slug for charity commission.

Data migration to update the organisation slug, and associated data,
create a redirect and reindex documents in search.

This also renames the org screenshot file so that it can continue to be found.

**Review only please.** This will need to be merged in a co-ordinated fashion with all the other places the slug has to be updated.
Did we get rid of the test that enforces 1.9 hash-syntax?