js_separation branch: chart does not move in generated htmls

[veghdev]

With the new separated js class in the generated htmls the chart displayed after the first cell, and not moved (display="actual")
Even with manually saved ipynb output, even if nbconvert generated it.

Example:

cd tools/html-generator

with execute flag *if output not created and saved manually:
../../.venv/bin/jupyter nbconvert --Exporter.preprocessors=preprocessor.NbPreprocessor --to html --execute ../../docs/tutorial/sorting.ipynb

without execute flag *if output created and saved manually:
../../.venv/bin/jupyter nbconvert --Exporter.preprocessors=preprocessor.NbPreprocessor --to html ../../docs/tutorial/sorting.ipynb

[simzer]

This seems to be a bug in nbconvert. I have reported this issue: jupyter/nbconvert#1759

Meanwhile, we should switch back to generating divs with a unique id for ourselves for the time being.