BERLIN (Reuters) - A dispute between the Spanish government and the leaders of Catalonia over the region s efforts to seek independence could only be solved through talks based on the Spanish constitution, German Foreign Minister Sigmar Gabriel said on Wednesday.  A unilateral declaration of Catalonian independence would be irresponsible,  Gabriel said in a statement.  A solution can only be found through talks on the basis of the rule of law and within the framework of the Spanish constitution.  