Just released an OpenGL viewer with higher FPS for large trees

[ErikOrjehag]

Hello guys, the py_trees_ros_viewer has served me well for a long time but I've recently run in to low FPS issues visualizing larger trees. So I just started on a OpenGL based viewer over here (https://github.com/DynoRobotics/py_trees_ros_gl_viewer) that I thought that you might be interested in. It's very early stage and lacks a lot of the features that py_trees_ros_viewer provied, but it's a start and if you want to contribute please feel free :)