Deleting all filtered elements should be restricted to users with admin access

The Delete worker results and Delete buttons in the actions menu are restricted to users with admin access, but the Delete all button when browsing a project or a folder is enabled for users with contributor access. Trying to use it while being only a contributor results in a backend error ("You do not have admin access to this corpus"). This button should just be disabled for users without admin access.

Found while working on #639 (closed)