update-manager - en to csb translation catalogue (3 entries)

note: TRANSLATORS: %s is a country
en: Server for %s
csb: Serwera dlô kraju %s

note: More than one server is used. Since we don't handle this case in the user interface we set "custom servers" to true and append a list of all used servers
en: Main server
csb: Przédny serwera

en: Custom servers
csb: Jine serwerë
