Add preferred language to user and language to redirect from request

Thanks for your MR! I like the idea, but I did some tests with the getLocale() method (since I didn't know that one) and for me it always returned "en" even though I was browsing the site in Dutch (nl).
Wouldn't it be better to store the current language in the state, so we can rely on that instead of the request object?

Hi @Matthijs yes, right getLocale not good here I changed it to LanguageManager, also I don't see any reason to use custom language negotiator in module so I removed. This is breaking all logic regarding localisation. With this patch user should add redirect_uri per language(and I guess need not to loose add this to documentation) like these:

en/oidc/login-redirect
de/oidc/login-redirect

And if user want to use one redirect uri need to write custom language negotiator with special logic.