erp5_data_notebook: moves variables and setup storage from ActiveProcess to `notebook_context` property

Notebook's variables and setup were being stored in an ActiveProcess, which is
not needed anymore, because now everything related to user context can be
safely stored in the ZODB.
They are stored in a `notebook_context` property of the Data Notebook
itself. Code and tests were updated properly. The old `process` property was removed.

All the references to *_variable_dict were renamed to  *_notebook_context, documentation
and tests were updated. Related objects like scripts and external methods were renamed
too.

To store objects in the `notebook_context` property we do 2 different tests: the first
to check if the object can be serialized by `ZODB.serialize.ObjectWriter`. If the first
test fails we test if the object can be serialized by cPickle. For the second test we
need to dump & load the object to be completely sure that it can be correctly loaded
later.

The function called by the Base_runJupyterCode external method was renamed from
Base_compileJupyterCode to Base_runJupyterCode be more consistent and avoid confusion.

All errors while running setup functions and now properly propagated to the user
interface in Jupyter and code execution is aborted.