Add operator shelf authorization, apply to relevant viewset, add command line tools for permissions management.

See the testing spec in the bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1074304#c1

r? @robhudson @ngokevin @diox
Yeah. I know the underlying SQL (`SELECT 1 FROM ...1) and return value (Boolean vs model object creation) is more efficient but the extra query may outweigh the benefit. I just like `exists` when dealing with booleans. No worries.