Deny/block access functionality

[akashdeep-singh]

As far as I understand the spec, we can allow agents access by WebID or grouping, but there is no explicit deny. I think that may be a useful feature. If I want to block a certain person from a resource by WebID, while it is publicly readable, that should be possible, and that seems to be the only use case for a deny. If I'm not using public access, then I can always create a group without that person's WebID (albeit that could end up polluting the list of groups). An explicit deny could work along with group access, as in "Colleagues" except John, where I want John to not see this particular resource but I don't want to remove him from the group either.

[csarven]

Thanks for raising this. I hope the use case is sufficiently acknowledged in this PR: https://github.com/solid/authorization-panel/pull/112 . Feedback welcome.