By Sedara Oluwadara   De Jong celebrated with team-mates after adding Barcelona's sixth goal against Pumas UNAM Frenkie de Jong "wants to stay" at Barcelona despite interest from Manchester United, says the club's president Joan Laporta.   The Premier League side agreed a £63.5m deal for the Netherlands midfielder, 25, last month, but the move is yet to be finalised.   De Jong came on at half-time and scored in Barcelona's 6-0 friendly win over Pumas UNAM on Sunday.   "He is a Barca player of great quality and we want him to stay," said Laporta.   "He has offers