* glom/application.cc:
* glom/dialog_existing_or_new.cc:
* glom/frame_glom.cc:
* glom/mode_design/translation/window_translations.cc:
  Use FileFilter via RefPtr.
* glom/bakery/app_withdoc_gtk.cc: Use RecentFilter via RefPtr.
* glom/mode_data/db_adddel/db_adddel.cc:
* glom/mode_data/placeholder-glom[h|cc]:
* glom/utility_widgets/flowtable[h|cc]:
* glom/utility_widgets/imageglom.[h|cc]: Change use of get_size() to
  get_preferred_size() and change on_expose_event() to on_draw().