Add Boolean argument to to urdf parser to select which geometry to load

  - collision or visual,
  - complete commit 75d6e55: read position of relevant geometry,
  - simplify internal API: pass links [i] to methods instead of links, i.
Rename setStaticTransform -> getStaticTransform.
Fix bug in box construction in urdf parser.

  - osg box parameters are half-lengths while urdf box parameters are lengths.
Throw exception if parser failed to read urdf file.
Add parameter linkOrObjectFrame to function urdfParser::parse.

  - this parameter determines whether the node position is the urdf link
    position or the position of the object attached to the link.