Added loading objects dialog with progress and cancel.
* src/main.c: Display window before loading command line specified projects. * gladeui/glade-project.[ch]: Added dialog that pops up when about to load a large project with glade_project_push_project() to push the progress and glade_project_load_cancelled() to check and abort while loading the project. * gladeui/glade-widget.c, gladeui/glade-widget-adaptor.c: Push progress and abort loading when project indicates the user cancelled the load.