Update Julia installation

• Upgraded to more recent version 1.6.0
• Eliminate Jupyter package IJulia. It can only be installed by end-user with lots of other Julia packages Installed with:

  julia -e 'import Pkg; Pkg.add("IJulia")'
  julia -e 'using IJulia; installkernel("julia")'

  in $HOME/.julia and $HOME/.local/share/jupyter
• Use packages on the LCG stack whenever possible