* glom/utility_widgets/imageglom.[h|cc]: Move scale_keeping_ratio() to
glom/utils_ui.[h]cc] as Utils::image_scale_keeping_ratio().
* glom/utility_widgets/canvas/canvas_image_movable.cc:
* glom/utility_widgets/db_adddel/db_adddel.cc:
* glom/utility_widgets/flowtable_dnd.cc: Adapted.