Modified joint names

Added the prefix "jaco_" to the joint names to match with the urdf. It allows to see the arm correctly in rviz.
Urdf model updated from xacro

This is the updated urdf model from the new xacro file.  The y angle have been inverted from a previous pull.
Merge pull request #18 from jpmerc/patch-1

Modified joint names
Merge pull request #19 from hommeabeil/patch-1

Urdf model updated from xacro
Added jaco-ros metapackage