Brighton have agreed a deal to sign highly-rated Nigerian winger Zadok Yohanna from AIK Stockholm for £21.5 million.The 18-year-old is expected to complete the move when the summer transfer window opens on June 15, signing a five-year contract with the Premier League club.Brighton manager Fabian Hurzeler welcomed the youngster's arrival, describing him as an exciting attacking talent with the ability to influence matches in the final third."I'm looking forward