Implement ability to restrict datasets to specific teams

[paulthatjazz]

Upcoming datasets (Soil, Hedgerows) are under restrictive licenses. In order to ensure that these are not publicly available, we need a setting to enable access to a specific team.

Likely implementation:

1. New table Permissions 1:M (team:permissions) with string value (name) and bool value (enabled) for each team.
2. Flag field on Team table.