Silence gtkmm warnings when compiling with clang.

The following are the silenced warning, which showed up in each compiled
GUI code object:

==========
In file included from /home/jagerman/research/creativity/creativity/gui/InfoWindow.cpp:2:
In file included from /home/jagerman/research/creativity/creativity/gui/GUI.hpp:10:
In file included from /usr/include/gtkmm-3.0/gtkmm.h:251:
/usr/include/gtkmm-3.0/gtkmm/stack.h:124:8: warning: 'Gtk::Stack::add' hides overloaded virtual function [-Woverloaded-virtual]
  void add(Widget& child, const Glib::ustring& name);
       ^
/usr/include/gtkmm-3.0/gtkmm/container.h:167:16: note: hidden overloaded virtual function 'Gtk::Container::add' declared here: different number of parameters (1 vs 2)
  virtual void add(Widget& widget);
               ^
In file included from /home/jagerman/research/creativity/creativity/gui/InfoWindow.cpp:2:
In file included from /home/jagerman/research/creativity/creativity/gui/GUI.hpp:10:
In file included from /usr/include/gtkmm-3.0/gtkmm.h:251:
/usr/include/gtkmm-3.0/gtkmm/stack.h:137:8: warning: 'Gtk::Stack::add' hides overloaded virtual function [-Woverloaded-virtual]
  void add(Widget& child, const Glib::ustring& name, const Glib::ustring& title);
       ^
/usr/include/gtkmm-3.0/gtkmm/container.h:167:16: note: hidden overloaded virtual function 'Gtk::Container::add' declared here: different number of parameters (1 vs 3)
  virtual void add(Widget& widget);
               ^
2 warnings generated.
==========
Got rid of Event::Type::new_states_acknowledged.

This was simply redraw_complete (before the recent GUI overhaul to
display states), which was used to synchronize redraws due to the redraw
dependency on the live simulation status.  Since everything now only
depends on states, which are fixed once created, this synchronization is
no longer needed.
Added documentation for ReaderStore.columns
find() hint is now used as the starting point.

Previous to this change, find(..., hint) was checking members_[hint],
and returning it if matched, otherwise starting a linear search from 0
through members_[members_.size()-1].  This commit changes that behaviour
to use two iterators to iterator outward starting from [hint], thus
checking [hint], [hint+1], [hint-1], [hint+2], [hint-2], etc.  until the
target is found, or everything has been checked.
Fix segfault viewing uninitialized visualization