Multi-Spring patch.

This change allows creating multiple connections
between nodes, with specific anchor points that
differ from the actual origin position of the node.

The spring's displacement and force vector is calculated
between the anchor points, which always maintain their
relative position to the origin.
The spring's force then acts on the origin.
Merge branch 'master' into multisprings

Conflicts:
	src/main/java/layout/PhysLayout.java
Add an example for multiple springs.

There are two balls connected by many springs with
random anchors. Individually, the springs only seek
to maintain equilibrium length, and rotate freely.

Taken together, the springs act like a flexible rod
that forces the two balls to maintain both relative
distance and angle.

Moving the balls and reconnecting will make their current
relative position the new equilibrium.