Change dependency python3-opengl to freeglut3

[bafu]

We are using PyOpenGL and PyOpenGL-accelerate wheels, which needs freeglut3 to prevent the error

[D 200412 12:31:43 __init__:13] Subscribe topic berrynet/engine/ovdetector/result
Traceback (most recent call last):                                                 
  File "berrynet/client/fbdashboard.py", line 347, in <module>           
    main()                                                                 
  File "berrynet/client/fbdashboard.py", line 331, in main              
    glutInitWindowPosition(0, 0)        
  File "/home/bafu/.local/lib/python3.6/site-packages/OpenGL/platform/baseplatform.py", line 425, in __call__
    self.__name__, self.__name__,                                                                              OpenGL.error.NullFunctionError: Attempt to call an undefined function glutInitWindowPosition, check for bool(gl
utInitWindowPosition) before calling                  

Currently freeglut3 is included by installing python3-opengl.