Respect locales mapping

[dmitrybubyakin]

app('config')->set('laravellocalization.localesMapping', [
    'en' => 'custom',
]);

// Route::prefix(app(...)->setLocale()) => http://localhost/cusom => custom
$this->assertEquals('custom', app('laravellocalization')->setLocale('custom'));
// Current locale is en
$this->assertEquals('en', app('laravellocalization')->getCurrentLocale());

// both are in supported locales
$this->assertTrue(app('laravellocalization')->checkLocaleInSupportedLocales('en'));
$this->assertTrue(app('laravellocalization')->checkLocaleInSupportedLocales('custom'));

// use the mapping
$this->assertEquals('http://localhost/custom/some-route', app('laravellocalization')->localizeURL('some-route', 'en'));
$this->assertEquals('http://localhost/custom/some-route', app('laravellocalization')->localizeURL('some-route', 'custom'));

[mcamara]

Can you write this feature into the README and the CHANGELOG files?

I'll merge the PR after it, thanks a lot for your work!

[dmitrybubyakin]

@mcamara Thank you for great package!