Initial support for showing graph visualizations of state in seec-trace-view.

Add StateGraphViewerPanel, which uses  the existing support for creating dot
graphs from SeeC-Clang Mapped process states, performs layout and rendering
using the Graphviz library, and displays the result in a wxWebView (the graphs
are rendered to SVG).

Also include <utility> in ScopeExit.hpp as it uses std::move().

Note: we need to package the Graphviz dynamic libraries into the Mac OS X
application bundle.