Add support for organization roles

[ruuda]

Recently GitHub has added organization roles. This means that our default access settings don’t need to be enforced specifically for every repository, we can have an organization default.

But then in GitHub Access Manager, we need to:

• Make sure to take those new access settings into account when scanning repositories, I’m not sure how it manifests in the API.
• Have a way to verify the organization roles and role assignments, if that is possible through the API at all.

[ruuda]

It seems that in checking repository access, the API returns both access that is configured at the repository level, as well as access inherited from the organization, so we don’t need to do anything special there!