R1:329d03661f3b

Use an extended policy to bind column and board policies together

Summary:
Ref T10349. Columns have the same policies as the projects they belong to.

However, the current implementation just returns the policy directly. This usually works, but if the project has a policy like "Members of (This) Project", the policy filter tries to check if the viewer is a member of //the column itself//. That doesn't work, since columns don't have members. This leads to a situation where columns on "Editable By: Project…