Make permissions also accessible under /config

Might be no longer relevant with revamped IA, but nonetheless.

See parent issue at #715972: People section(s) are very confusing. Copy/pasting comment from Jeff:

1. There's seems to be significant confusion around finding permissions. I do think so long as there's a 'people' primary toolbar menu, grouping 'permissions' with 'people' is a sound idea. The problem is many people, both new and existing, can't find 'permissions.' I think in their mind, 'permissions' is a preference-like setting, and therefor try 'configure' first. As such, we should cross-link from config.

2. For those that have TAC installed, it's awfully strange that /config/people provides a link to granular-level access control, yet not site-wide permissions.