Adopt Nls PSR-4

[ralflang]

Nls is used in IMP_Compose::_getAutoSendLanguages - Use Horde\Nls\Nls::languages() instead
Nls is used in IMP::numberFormat - Use Horde\Nls\Nls::getLocaleInfo() instead
Nls is used in config/prefs.php getLanguageISO - Use Horde\Nls\Nls::languages() instead

See https://github.com/horde/Nls/blob/FRAMEWORK_6_0/doc/UPGRADING.md