Created a grasper robot with RobotGrasper class.

This class just define an abstract robot with the grab_ service.
The main goal of this class is to avoid code duplication.
[doc] {laas->morse}-theme + rm old files
[doc] change CSS for <tt> to make it more obvious
[doc] mention OpenRTM in install
[doc] Improved rendering of line num in doc code samples
[doc] Improve CSS for images. Honor :align center:
[doc] Minor change to CSS for admonitions