Cleanup and add more actions to main menu

modules/gui/pymod/CMakeLists.txt

modules/gui/pymod/__init__.py

modules/gui/pymod/dng/init.py

modules/gui/pymod/dng/menu.py

modules/gui/pymod/export_gosty.cc

modules/gui/pymod/init_menubar.py

modules/gui/pymod/scene/init_inspector.py

modules/gui/src/gosty_app.cc

modules/gui/src/gosty_app.hh

modules/gui/src/perspective.cc

modules/gui/src/perspective.hh

modules/gui/src/widget_geom_handler.hh