It hosted World War II troops and the Rolling Stones. Retro rides and a roller disco. There was even a public campaign to turn it into a heritage site. But it’s the dealings of a veteran hedge fund manager that’s drawing new attention to Britain’s oldest surviving amusement park. Nick Niell, the man behind Arrowgrass Capital Partners, was snapping up properties worth millions of pounds around the Dreamland resort in the seaside town of Margate just as his hedge fund was pouring client money into an effort to revitalize the attraction.