forward declarations are our friends

modules/gui/pymod/export_gosty.cc

modules/gui/pymod/export_perspective.cc

modules/gui/src/file_loader.cc

modules/gui/src/gl_win.cc

modules/gui/src/gl_win.hh

modules/gui/src/gosty_app.cc

modules/gui/src/gosty_app.hh

modules/gui/src/messages/message_box_widget.cc

modules/gui/src/panels/tabbed_panel_bar.cc

modules/gui/src/perspective.cc

modules/gui/src/perspective.hh

modules/gui/src/scene_selection.cc

modules/gui/src/tools/tool_bar.cc