solved ancestry revisualization problem which caused two pieces to be wrongly marked as root nodes, instead of one.
ancestry tracker: added logging and refactored
revisualize_ancestry.py: lines between generations grow rather than appearing out of nowhere
modified ancestry revisualization colllection
trying to remove an aesthetic glitch in some ancestry revisualizations, e.g. utvandrarna-02, where nodes were connected too abrubtly. solved by imposing a time limit on tracked growth, so that "long growth" is instead divided into generations, between which lines are grown.