Added the calls necessary to manage path constraints. This commit
dependts on the changes commited to moveit_ros package to have access
to this functionalities.

Bassically now is possible to set the constraints as a moviet_msgs
Constraint message and retrieve an instance of the current path constraints
for a group.
Merge pull request #19 from ibec-robotics/set_and_acces_path_constraints

Added the calls necessary to manage path constraints. This commit