ACCRA, GHANA — Polls opened in presidential and legislative elections in Ghana on Saturday, poised to be a litmus test for democracy in a region shaken by extremist violence and coups. Some 18.7 million people are registered to vote in the West African country hit by one of the worst economic crises in a generation. However, the two main candidates offer little hope for change for the nation. Ghana used to be a poster child for democracy in the region. At a time when coups threatened democracy in West Africa, Ghana has emerged as a beacon of democratic stability with