[Debug] Fixed a problem in using spyder with python3

Same problem as in https://github.com/Ultimaker/Cura/issues/385

Fix:

My PR #387 based on #131 fixes the problem + installing python3-opengl

(1)

1. ldconf -p | grep libGL.so
   I found that the first entry was still
   libGL.so (libc6,x86-64) => /usr/lib/x86_64-linux-gnu/libGL.so
   instead of
   libGL.so (libc6,x86-64) => /usr/lib/nvidia-340-updates/libGL.so
2. cd /etc/ld.so.conf.d
   I found many conf files, including
   i386-linux-gnu_GL.conf and x86_64-linux-gnu_GL.conf
   cat x86_64-linux-gnu_GL.conf
   /usr/lib/nvidia-340-updates
   /usr/lib32/nvidia-340-updates
   but i386-linux-gnu_GL.conf is empty.
   So I just copied the contents in x86-linux-gnu_GL.conf to i386-linux-gnu_GL.conf
3. sudo ldconfig
   Everything is OK now

(2)

　　　　　　sudo apt-get install python3-opengl