By Noah Barkin BERLIN (Reuters) - Returning from her summer break in mid-August, German Chancellor Angela Merkel raised some eyebrows by describing Europe's refugee problem as a bigger challenge than the Greece crisis, which had overshadowed all else in the first half of 2015. No one in Germany is questioning her assessment any longer. In the past two weeks, the country has been shaken by a perfect storm of headlines that have elevated the refugee issue, long seen in Germany as primarily a southern European problem, to the very top of the public and political agenda.