improve encapsulation of file editor window object * file-editor-interface.h (file_editor_interface::connect_visibility_changed): New function. * file-editor.h, file-editor.cc (file_editor::handle_visibility, file_editor::focus, file_editor::connect_visibility_changed): New functions. (file_editor::construct): Connect main_window::new_file_signal to file_editor::new_file. * main-window.cc (main_window::editor_window): Rename from _file_editor. Change all uses. (create_default_editor): New static function. (main_window::main_window): Use it to initialize editor_window. (main_window::new_file_signal, main_window::open_file_signal): New signals. (main_window::new_file, main_window::open_file): Emit signals instead of calling file_editor functions directly. (main_window::focus_editor, main_window::handle_editor_visible): Delete. (main_window::connect_visibility_changed): Call editor_window->connect_visibility_changed. (main_window::construct): Don't create _file_editor. (main_window::construct_file_menu): Connect _open_action::triggered to editor_window::request_open_file instead of main_window::open_file. Connect _new_script_action::triggered to editor_window::request_new_file instead of main_window::new_file. (main_window::construct_new_menu): Connect editor_action::triggered to editor_window::focus instead of main_window::focus_editor.