To increase the user base of Cantor and to be able to benefit from the big amount of teaching and scientific material published and shared in Jupiter notebook format we need to support this format.

The format description can be found here
https://nbformat.readthedocs.io/en/latest/index.html

Similar to the current function Worksheet::load() where Cantor's native projects in XML format are loaded we need to add another function which will be able to load the JSON document, parse it and convert to Cantor's entities like CommandEntry, etc.

Most probably it won't be possible to load everything in the beginning. We need to identify the gaps and add the missing functionality to Cantor step by step.