[Menu] Class menu_view should have member of type view_mode

[kausmees]

Depends on:

• [x] #493

Same as in #494, but for class menu_view

• [x] Make test
• [x] Solve test

// (495) There should be a member of type view_mode
{
  menu_view mv;
  view_mode expected_next_view = view_mode::quit;
  assert(mv.what_next() == expected_next_view);
}

[TheoPannetier]

Done!