Improvements to exporting/writing the behavior graph.

* [QSIM_NG,FIX] The identification of duration/point states for vertex coloring was incorrect.
* [QSIM_BG,DOC] Added documentation.
* [QSIM_BG,EXT] Behavior graph printing now writes to the current output stream (was: debug stream).
* [QSIM_BG,EXT] Do not print the transitions header in case there are no transitions.
* [QSIM_BG,EXT] Print a separator in between state prints and after the last state print.
* [QSIM_BG,EXT] Use the new statement printed (i.o. the triple name printer).