Use cmake submodule

  - this method parses an urdf file and create a node for each object. The
    position of each node corresponds to the position of the corresponding
    object and not to the position of the link holding the object.

  - addUrdfCollision loads collision geometry in viewer, while
    addURDF loads visual geometry.

  - urdfPackage -> meshDataRootDir in addURDF.

  - throw exception if problem.

  - rename package gepetto-viewer-corba,
  - use lower case for filenames,
  - fix C++ client (without testing).

add LeafNodeLine.