Naman Ramachandran “Mangrove,” directed by BAFTA and Oscar winner Steve McQueen (“12 Years a Slave”), will open the 64th edition of the British Film Institute London Film Festival.Written by McQueen and Alastair Siddons, “Mangrove” is one of five films that make up the “Small Axe” anthology. Set from the late 1960s to the mid-1980s, the films each tell a different story involving London’s West Indian community.