Add a setting to override location-based disabling of Tor
Users in China have reported that Orbot works over Shadowsocks, and I've confirmed that Briar's Tor connectivity works over Shadowsocks using this app in VPN mode, with no configuration on the Briar side. The same should work in China, except that we disable Tor based on the user's location. We should add a setting to allow the user to override location-based disabling of Tor.