Created shape generator in simulation module

This pull-request is the second part of my GSOC 2014 project.
- Adds the shape generator to PCL within the simulation module.
- Added simulation to doxygen generation
- Added an example under pcl_example_shape_generator.
- Added two tools, generate_shape and convert2pcd
 - generate_shape uses instructions found in text files to assemble scenes and objects
 - convert2pcd can read stl and obj file and samples on the faces with a given point density and saves a pcd file (unlike obj2pcd it samples on faces rather than on the vertices, allowing constant point density).

![comparison_obj2pcd_convert2pcd](https://cloud.githubusercontent.com/assets/3592251/4207431/3d686a4e-3856-11e4-9a05-9360b3f0cfc3.png)



> So I guess using curvature, label and rgb would actually take the same amount of space as curvature and label

Yes, you are right. Though the fact that it is possible to add other fields does not necessarily mean that this is ought to be done. I would say let's wait until we face those other scenarios that need the complex type. But this particular contribution only needs `PointXYZLNormal`.