Issue: Access Masks

Per-user access masks for the wiki. The AdminCP page should allow admins to give users permissions on a per-area basis. This is already feasible due to the changes to permissions fetching and could be a simple extension of the permissions manager to pass the appropriate fields. Mainly needs an appropriate interface for management.

Also, access masks from VaultWiki 3 (though I don't think they worked as expected) should be imported.