It’s 20 years since the Good Friday Agreement was signed,- bringing power-sharing and much peace to Northern Ireland. But for all the progress, there are shadows over today’s anniversary. For more than a year, the DUP and Sinn Fein have refused to share power in Stormont. And there are hard questions over how to avoid a hard border with the Republic after Brexit. But today in Belfast the politicians who forged the agreement came together to celebrate it.