Pool-specific admin permissions

[liddiard]

Ideally we could restrict bot admins to perform actions relating to a specific pool only. This would require setting up a custom permission using Django's permissions framework, and it would probably also include extending the User model which could be a bit of work.

edit: Extending the user seems like more trouble than it's worth; probably better to just have a one-to-one model to store User permissions. See Option 2 here.