cleanup pending

[fopinappb]

• TLA field in dns_ips
• change to organisation? consider using a swappable model (like auth.User) to avoid migrations within the app?
• import_export mixin: add it globally to every admin model?
• move slack_display method to a model list setting from slackbot or add a register method - otherwise it's impossible to add it to 3rd party models

[gsilvapt]

For the first item, I'd vote for changing tla to organisation like we have for IPAdress.
For the second, I'm not sure what you were trying to achieve there 😛
For the last one, perhaps you wouldn't mind expanding on it a bit here?