Hydro

Hi! This should make for a working ROS Hydro version of the plugin, already updated to use catkin. 

I also added a fix to computeRotation, which failed to return a unit quaternion whenever the eigenvector matrix isn't a valid right-handed rotation matrix. This happens when we have repeated eigenvalues, and eigenvectors are returned in an invalid order.

I still haven't updated the nav_msgs::Odometry part, but it should be relatively straightforward from what I've done.