Begin adding the preview functionality in python2.7, not completed yet.

Samo Penic

2016-07-07 c89a71dbf5ce77d7accc60d8637f0eea64ecc1e6

 src/general.h

@@ -313,6 +313,7 @@
   ts_double R_nucleusX;
   ts_double R_nucleusY;
   ts_double R_nucleusZ;
   ts_double nucleus_center[3];
    ts_double area;
} ts_vesicle;