Get familiar with D3

D3 basic usage should be properly understood.
This includes:

• "scene composition"
  • elements selection/modification
  • control flow to be able to handle more complex cases
  • styling so it looks good (understanding how to animate stuff is optionnal but fun)
• data handling so viewer can be an interface between D3 way of doing things and HERA spec
• event management so viewers can be dynamic (user interaction, real time data update and so on)