FS#3558: Add firstname field for clients and resellers.

install/sql/incremental/upd_dev_collection.sql

install/sql/ispconfig3.sql

interface/web/client/form/client.tform.php

interface/web/client/form/reseller.tform.php

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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