Drop support for @person in favour of <@userid>

[nzlosh]

Slack changed how to uniquely identify users from the display name to user id. The #31 unittests branch includes a change which alters how user information in the Person class is reported and used.

To illustrate the change here is the whois output from the original slack backend:

┏━━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━━━━┓
┃ key      ┃ value                ┃
┡━━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━━━┩
│ person   │ `@nzlosh`            │
├──────────┼──────────────────────┤
│ nick     │ `nzlosh`             │
├──────────┼──────────────────────┤
│ fullname │ `Carlos`             │
├──────────┼──────────────────────┤
│ client   │ `DSKNFHVT5`          │
├──────────┼──────────────────────┤
│ email    │ `nzlosh@yahoo.com`   │
└──────────┴──────────────────────┘

The slackv3 unittests branch reports the following for whois

┏━━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━━┓
┃ key      ┃ value              ┃
┡━━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━┩
│ person   │ `UMV1SEYMA`        │
├──────────┼────────────────────┤
│ nick     │ `nzlosh`           │
├──────────┼────────────────────┤
│ fullname │ `Carlos`           │
├──────────┼────────────────────┤
│ client   │ `D018GUWHXN0`      │
├──────────┼────────────────────┤
│ email    │ ``                 │
└──────────┴────────────────────┘

The major difference is the person field shifts from @username to userid. User id's are meant to be wrapped in the form <@Uxxxxx> when highlighting a specific user. This change in the backend would impact existing plugins that depend on the @username behaviour that has been deprecated since 2017. For more information about this change see https://api.slack.com/changelog/2017-09-the-one-about-usernames

[jcfrt]

I have no idea what I'm talking about and I'm very tired after investigating for hours, but it seems to me that this "person" field being now a UUID broke some things, like the config file regarding who is admin of the bot they can't be matched by name anymore), and I get errors from errbot saying errbot.backends.base.UserDoesNotExistError: Cannot find user 'UUID_HERE whenever something involving a user is triggered.

Any idea if this is an errbot problem, a slack_sdk problem, or a backend-slackv3 problem?

[jcfrt]

Nevermind, I spoke too soon. There doesn't seem to be an issue. I cleared my cached data and the error doesn't seem to occur anymore.
I also fixed my admin issue: I erroneously added the UUID as "@uxxx" instead of simply "Uxxx".
It's still a bit annoying that logs display UUIDs now instead of usernames, but I guess this can be solved on errbot's side.