Add access to the viewer inside the window manager for handling events.

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

  - osg box parameters are half-lengths while urdf box parameters are lengths.

  - collision or visual,
  - complete commit 75d6e550: read position of relevant geometry,
  - simplify internal API: pass links [i] to methods instead of links, i.

  - parameter collisionOrVisual selects "collision" of "visual" parts of
    link description.

Add getColladaPtr to access the internal osg::Node structure + indent.

This commit allows accessing the internal osg::Node structure
necessary to access the underlying geometry of the collada structure.
It also indent the code following a 2 spaces strategy.

  - in urdfParser::parse, package_path -> meshDataRootDir

  - -lgepetto-viewer was missing in the pc file.

Add setScale (vector3d) for Node.

Conflicts:
	src/Node.cpp

  Graphics -> graphics.

  - conversion may alter value,
  - unused parameter.

  - rename package gepetto-viewer (after short discussion with Justin C.),
  - use lower case for filenames,
  - reorganize headers.