Some verbiage change to outputs (plus a couple of comments)

[PromoFaux]

What does this PR aim to accomplish?:

Replaces some printed usages of white/blacklist with allow/deny as per other areas of the software.

Actually, thinking about it, we can probably pull out the legacy pre v5 file pointers/helpers now?

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[PromoFaux]

The final commit is optional - but I think we can probably do away with this at this stage

[PromoFaux]

Reverted the final pre-v5.0 migration commit for now. Probably needs addressing as part of a larger patch later

[yubiuser]

Reverted the final pre-v5.0 migration commit for now. Probably needs addressing as part of a larger patch later

If we remove those migration steps, users still on v4 won't be able to upgrade to v6 (as they have no chance to get to v5 first once v6 is is 'master' everywhere). I'm not sure how many users will be affected, the number might be rather small.