WIP: Fix problems with javascript and plotly output

I added some protective <div>'s around crucial code. This fixes the output problems for my current cases.

Open questions:

• One display_data output can have several entries in the data dictionary. Is this treated correctly now? Or do we need to loop over output.data?
• One cell can have several outputs. I noticed that this causes problems with thebelab, showing the cell source code several
  times according to the number of outputs. Can this be fixed?
• The template has nothing for execute_result output. Should we add this?