[WIP] Have openPMD-viewer slider work in Google Colab

[RemiLehe]

This makes a few changes to have openPMD-viewer work in Google Colab.

• When using %matplotlib widget, Google Colab renames the widget backend as 'module://ipympl.backend_nbagg'
• The Accordion widget is not working (see Custom widget manager breaks Accordion widget googlecolab/colabtools#3571) ; thus this avoids displaying the accordion

Note that, in order to setup the environment in Google Colab, I had to use the following code in the first two cells:

# Install required packages
!pip install git+https://github.com/openPMD/openPMD-viewer@enable_colab --quiet
!pip install ipympl --quiet
# Restart notebook so that the new packages are available
# This will raise a message saying "Your session crashed for an unknown reason", but simply ignore it
get_ipython().kernel.do_shutdown(restart=True)

# Enable interactive widgets in Colab
from google.colab import output
output.enable_custom_widget_manager()
%matplotlib widget