VOTERS in Africa's biggest economy and most populous nation are heading to the polls on February 25 to elect a new president and lawmakers amid growing frustration over unprecedented insecurity, industrial-scale oil theft and surging inflation. President Muhammadu Buhari, who will complete his constitutionally allowed two terms in May, is not on the ballot. Voters will also choose new senators and members for the House of Representatives. Governorship races follow on March 11 Here is what you need to know about the election. WHO IS RUNNING? A total of 18 candidates are vying for the presidency. But the main contest…