Properly identify language on start

Could you use the builtin [app.getLocale()](https://github.com/electron/electron/blob/master/docs/api/app.md#appgetlocale) function to get the language on app start instead of `navigator.language` in [LocalSettings.js](https://github.com/OpenBazaar/openbazaar-desktop/blob/master/js/models/LocalSettings.js#L38)? It didn't detect my language `pl` and it first started with the `en-us` version,