#137 borderWidth in Layout should be a variable

[Brunni]

There is a problem when using big Vertex-Icons because they dont fit in the Window.

In FRLayout. java line 201 the borderwidth is calculated by
double borderWidth = getSize().getWidth() / 50.0;

This may work for some kind of icons. But for my Vertex-Icons with 64x64 it didn't work. The nodes werde outside of the visible area.
I had to manually set borderwidth to 70.

Proposal:
Introduce a function like setBorderWidth in all Layouts. Or improve Calculation of borderwidth.