use shortcut manager for the main help menu * main_window.cc (add_action): new parameter for the signal receiver; (construct_help_menu): use add_action for the actions of the menu; (construct_documentation_menu): use add_action for the actions of the menu; (set_global_shortcuts): set/unset shortcuts * main-window.h: actions are class variables, add_action with new parameter * shortcut-manager.cc (do_init_data): initialize the shortcuts in the help menu

EXTRA_DIST += \
  m4/module.mk \
  m4/ax_blas.m4 \
  m4/ax_blas_f77_func.m4 \
  m4/ax_compare_version.m4 \
  m4/ax_lapack.m4 \
  m4/ax_pthread.m4 \
  m4/gnulib-cache.m4 \
  m4/libtool.m4 \
  m4/ltoptions.m4 \
  m4/ltsugar.m4 \
  m4/ltversion.m4 \
  m4/lt~obsolete.m4 \
  m4/pkg.m4