Image fields: Add Open, Open With, and Save context menu items.
* glom/utility_widgets/dialog_image_save_progress.[h|cc]: * ui/operator/dialog_image_save_progress.glade: Added a progress dialog to do image saving, though it does not yet do async saving so the dialog is never shown. * Makefile.am: * Makefile_glom.am: * po/POTFILES.in: Mention the new files. * glom/utility_widgets/imageglom.[h|cc]: Add the new context menu items, using a temporary file for the Open and Open With features. Open With uses AppChooserDialog to offer a choice to the user. Bug #630057