Target Margin Theater’s production of Eugene O’Neill’s Mourning Becomes Electra signals its nonconformist nature by having its audience to gather outside the Abrons Art Center, packed together like rush-hour travelers. The production, which is part promenade, rejects the usual, classical interpretation of O’Neill’s trilogy, which has often proved difficult to pull off. But director David Herskovits, in his progressively exhilarating realization of Mourning Becomes Electra, comes close to throwing off the curse.