Fix regression in frequencies to stations drag & drop

Since mode  dependent frequencies  were added the  MIME type  for drag
from the FrequenciesList model has been broken. This change fixes that
and  adapts the  StationList model  to  accept the  amended MIME  data
drops.

git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@6096 ab8295b8-cf94-4d9e-aec4-7959e3be5d79

FrequencyList.cpp

@@ -551,7 +551,7 @@ QMimeData * FrequencyList::impl::mimeData (QModelIndexList const& items) const
     {
       if (item.isValid () && frequency_column == item.column ())
         {
-          stream << QString {data (item, Qt::DisplayRole).toString ()};
+          stream << frequency_list_.at (item.row ());
         }
     }