some experiement with JointDef
framework/j2d/VertexTestDraw.java
Drawing polishing.
Vertex is now clean, solid circle with no axis in it.
Keyboard even re-wiring so we get more information when
keyboard event happens
Also, drawObjectString() is now moved into VertexTestDraw.
Having it declared abstract function DebugDraw caused
jbox2d-testbed-jogl compilation error.
Also, now we have our own draw code tucked in VErtexTestDraw,
this function doesn't have to on upper classes either.
Fixed a bug of creating a bombshell when clicking on a vertex
with shift key held.
Also, did some code clean up.
Now we can select edge!
Using simple math:-), because box2d didn't help us
find a joint based on a point.
1. Double click on the edge to change the weight
2. Changed the drawing code so we draw the weight of edge,
   no label.
Merge pull request #16 from karpark/UIRefinement1

Enhancements on user interaction on the graph objects