migration to catkin

Hi, I needed to use you library on a catkin project so I created a new package.xml file and slightly modified the CMakeList.txt. I thought that it should be able to be compiled without ros so I set this new behavior to be activated with a flag in the CMakeList.txt file which is set to false as default. Also I tried to keep the same info from the manifest. 

I am not sure if Makefile.ros is still useful and the link to http://ros.org/wiki/opengv is broken.

Cheers,
Quim