replace literal strings by symbolic constants for shortcut preferences * QTerminal.cc (doc_on_expression): sc_value already returns a string now * documentation.cc (notice_settings): replace literal key names by symb. constants of complete pref structure * dw-main-window.cc (notice_settings): replace literal key names by symb. constants of complete pref structure * gui-preferences-sc.h: add constant sc_pref stuctures for all shortcuts * gui-preferences.h: define a string constant for the shortcut setting group * gui-settings.cc (sc_value): use new method sc_def_value for getting the default value, already returning the shortcut as string (sc_def_value): new method for reading the default value from the shortcuts preferences structure * gui-settings.h: new method sc_def_value, sc_value returns a string * file-editor.cc (handle_enter_debug_mode, handle_exit_debug_mode, set_shortcuts): replace literal key names by symb. constants of complete pref structure * main-window.cc (notice_settings): replace literals by symbolic constant (configure_shortcuts): replace literal key names by symb. constants of complete pref structure * settings-dialog.cc (settings_dialog, write_changed_settings): replace literals by symbolic constants * shortcut-manager.cc (init_data): move all constants into gui-preferences-sc.h, update calls to init (), which now takes complete sc_pref structure as second argument; (write_shortcuts, fill_treewidget, import_shortcuts): replace literals by symbolic constants; (init): only two arguments, second argument gets complete pref structure; (set_shortcut, shortcut): takes complete shortcut structure as second argument instead of key name * shortcut-manager.h: init, set_shortcut, shortcut with new argument types