Ff fix qgfraction map

I had some problems in running this routine to extract the quark/gluon fraction map. In the loop over several channels this line doesn't provide the expected outcome:

L246: h_map.insert( std::pair<std::string, TH2D* >( orig_name, h ) );

Since origin_name is the same for all channels, the first value inserted in the map never change. I added the cleaning of the maps and now the code gives the expected result, with a different map stored for every channel.