Work on urdf2graspit package and C++ API

In the last weeks I have refined the urdf2graspit package which allows users to convert from URDF to the format used in GraspIt. It is now ready to be used.

The original GraspIt code now compiles with catkin – it is not necessary any more to use qmake.

I have also added a test C++ API interfacing the GraspIt planning algorithms. The main task was to rewrite some code such that the planner can be run without the graphical interface, and to write a C++ interface to load the robot and object files and to do the planning. This required some changes in the original GraspIt source, but I tried to keep the changes as minimally invasive as possible. The C++ interface is only a test at this stage and will be further developed into a final version in the next weeks.