Don't start Tor in countries that are known to block it

See the javadoc for getCurrentCountry for details on how we get the country. In particular, it seems Google already has a hidden SystemService that does this, but we can't use it so we have to code our own. Luckily the solution I came up with independently yesterday almost exactly matches what they do.

Also, the hardcoded list of countries that block tor is incomplete; I will try to find a more complete list.

- fallback to SIM card before phone locale
- add disabled code to lookup the country from GPS, disabled because it requires a network call

- this will be useful later for e.g. auto-disabling Tor

There's currently no way to set this setting, so the bug isn't fixed.

Fixes bug #42.

Of course, not all devices support Bluetooth...