hydro compatibility

I don't think github allows suggesting a pull to a new branch, but that's what I'm trying to do here - these commits make fovis hydro compatible. Libfovis was fine and didn't need any adjustment, by the way.

These are only minor updates to make fovis_ros compile with hydro's new PCL.

I also added a launch file that works out of the box with openni_launch - something changed in hydro so the depth image was encoded in a way fovis can't deal with.