* glom/application.cc: Set default window icon.

* glom/dialog_existing_or_new.cc:
* glom/filechooser_export.cc:
* glom/frame_glom.cc:
* glom/glade_utils.h:
* glom/mode_design/script_library/dialog_script_library.cc:
* glom/mode_design/translation/window_translations.cc:
* glom/mode_design/users/dialog_groups_list.cc:
* glom/utility_widgets/filechooserdialog_saveextras.cc:
* glom/utils_ui.cc:
* glom/window_boxholder.cc:

Don't call set_icon_name() on individual windows.