Known issues:

* gtk_dialog_run is bad as it stops the GNUnet scheduler loop as well;
  => we should replace all calls to it by non-modal dialogs
  => the globals (builder in particular!) in the respective
     source files must be de-globalized, since we can then get two
     windows of the same type open at the same time (!)
  => additional advantage: ability to have multiple search/publish dialogs open at the same time!