Compatibility with ROS melodic on Ubuntu 18.04

[lebarsfa]

Hello,

I could not find a way to get a version of visual or vpython to work easily with ROS melodic on Ubuntu 18.04 (visual was working well with ROS kinetic on Ubuntu 16.04), so I made a branch https://github.com/lebarsfa/visual/tree/bionic to try to solve that. Unfortunately, there are breaking changes dues to numpy and boost so it should probably stay separate from the default master branch.
Do you think it could be good to add a bionic branch to the vpython/visual repo where I could make a pull request specific to Ubuntu 18.04?