Resurrect SSID block list

@hannosch had convinced me that client-side filtering of ad hoc networks and mobile device SSIDs was an unnecessary optimization because the server must detect moving APs anyways. But I've changed my mind on the mobile device SSIDs because the server-side detection will not be perfect and the client can easily detect (some) mobile devices.

I still agree that we don't need to filter ad hoc networks because there are quite a few stationary ad hoc networks (and the mobile ones should get filtered by the SSID block list or server-side moving AP detection).