BERLIN (Reuters) - German policymakers see a way out of the challenge posed by their top court to the European Central Bank's flagship policy programme that could even make the euro zone more robust -- but they need the ECB to play along.The German Constitutional Court last week gave the ECB three months to explain the proportionality of its bond purchases or risk losing Germany's Bundesbank -- one of 19 national central banks that are members of the ECB -- as a participant. It also called on..