Update nl language (take from ispconfig.bb-hosting.org) and merge

interface/web/admin/lib/lang/nl.lng

interface/web/admin/lib/lang/nl_language_add.lng

interface/web/admin/lib/lang/nl_language_list.lng

interface/web/admin/lib/lang/nl_software_package_list.lng

interface/web/admin/lib/lang/nl_users.lng

interface/web/client/lib/lang/nl.lng

interface/web/client/lib/lang/nl_client.lng

interface/web/client/lib/lang/nl_client_template.lng

interface/web/client/lib/lang/nl_client_template_list.lng

interface/web/designer/lib/lang/nl_module_show.lng

interface/web/dns/lib/lang/nl_dns_a_list.lng

interface/web/dns/lib/lang/nl_dns_soa_list.lng

interface/web/dns/lib/lang/nl_dns_template_list.lng

interface/web/mail/lib/lang/nl.lng

interface/web/mail/lib/lang/nl_mail_blacklist.lng

interface/web/mail/lib/lang/nl_mail_content_filter.lng

interface/web/mail/lib/lang/nl_mail_domain.lng

interface/web/mail/lib/lang/nl_mail_user.lng

interface/web/mail/lib/lang/nl_spamfilter_policy_list.lng

interface/web/mail/lib/lang/nl_spamfilter_whitelist_list.lng