Use libcgraphviz
add libcgraphviz
StateMachine: Pass font prop to individual items

This makes it possible to configure the font by changing StateMachineViewerWidget::m_font
Replace the primitive QtCore library detection with something more powerful.

No more hard-coded version numbers all over the place, and far less
false-positives.
Fix Windows build.
Prevent adding transtions where states are not added
show targetless transitions
increase font size
Merge branch 'libcgraph' into dev