Added toolbelt circle to resize the nodes by dragging

1) Resizing is done in discrete steps, in both directions
2) Visual effects appear on hover toolbelt
3) Dragging and making connections still operational
Fixed placing arrow heads w.r.t inner circle radius
Altered link distance in force layout to depend on radius of target and source
Made resizing more smooth
Merge branch 'master' of https://github.com/wouterbeek/WebQR