Add given_name and family_name claims to UserInfo

[ThoFrank]

The name splitting is using what was already implemented in nc for the
system address book

implements #506

[ThoFrank]

I looked a bit into the nextcloud code itself and found that the name splitting could be reused.
I tested it for my use case and it seems to work good enough. Of course this could be done a lot better. It even says so in the nc code:

public function splitFullName(string $fullName): array {
	// Very basic western style parsing. I'm not gonna implement
	// https://github.com/android/platform_packages_providers_contactsprovider/blob/master/src/com/android/providers/contacts/NameSplitter.java ;)