added move_group python interface bindings to move group interface
function:
void setPathConstraints(const moveit_msgs::Constraint &constraint)
in order to be able to set path constraints from python scripts
directly and no need to use the DB.
Retrieve from the movegroup the current path constraints

now it is possible to retreve as a moveit_msgs::Constreints
the current path constraints for a group to be hable to maniputlate
them from cpp. Function is:

moveit::planning_interface::MoveGroup::getPathConstraints() const

This function is also added to the python bindings in order to
be ussable for python and moveit_commander package.

fixed a incohrence in naming the python call for set the constrains
from a msg object.

Addd bindings to this functionality to the python wraprre
added a little more vervose documentation
Merge pull request #438 from ibec-robotics/add_functions_to_python_bindings

Add functions to python bindings