RadioBrowser: support for local/preferred country

Hello, this little change add two options for having a shortcut to local radios.

Either add a ipinfo token or set the preferred country

example:

radio-browseripinfotoken = my-token

The country will be chosen automatically.

Or, explicit and easier:

radio-browsercountry = FR

Set preferred country to FR (France)

Let me know if you like the change!

Thank you.