implement remote loader logic in Python

modules/gui/pymod/CMakeLists.txt

modules/gui/pymod/dng/init.py

modules/gui/pymod/dng/menu.py

modules/gui/pymod/export_file_loader.cc

modules/gui/pymod/export_remote_site_loader.cc

modules/gui/pymod/init_menubar.py

modules/gui/pymod/scene/file_loader.py

modules/gui/pymod/scene/loader_info_handler.py

modules/gui/pymod/scene/loader_list_model.py

modules/gui/pymod/scene/loader_manager_widget.py

modules/gui/pymod/scene/remote.py

modules/gui/pymod/wrap_gui.cc

modules/gui/src/CMakeLists.txt

modules/gui/src/file_loader.cc

modules/gui/src/file_loader.hh

modules/gui/src/loader_manager.cc

modules/gui/src/loader_manager.hh

modules/gui/src/remote_loader.cc

modules/io/pymod/CMakeLists.txt

modules/io/pymod/__init__.py