BRADENTON — It’s hard to imagine Bradenton without the Manatee Players Riverfront Theatre.For 60 years, starting with its inaugural production of the sentimental “I Remember Mama” and ending with its exuberant staging of “A Funny Thing Happened on the Way to the Forum,” the theater has been an essential element of its city’s geographical, social and cultural landscape.”A lot of us younger people, we grew up here,” said 16-year-old Nick Drivas, who has performed in several Players shows at the Riverfront Theatre. “There are a lot of memories here.”