Polygons and polylines top and left property precedence

As discussed in #1607 top and left specified in the options override the top and left calculated.
Please check the changes in polylines contructor to see if are accetable.

We could teocrically derive polyline classe from polygon class and just write one or two differente methods , for lot of things the class are the same, one is closing the path in the rendering , the other not.
Let me know if you want to unify them.