erp5_data_notebook: Add script for renderjs-extension

This commit adds server-side functionality for the jupyter-renderjs-extension. This has no interaction/impact with the existing functionality of the erp5_data_notebook BT.

@klaus mentioned that it is not common practice to return objects of a class (defined in the script). However, for usuability reasons there is an argument to do it here: Usually when using a jupyter extension, a module is imported an functionality is provided by that module. For instance:

In [1]:
import mymodule as mm
mm.someFunction()
mm.someOtherFunction()

To emulate this behavior and to be consistent with the ipython-version (Python 2 Kernel) of this extension I therefore use an object of the class RJSExtension which is returned by this script. I am then able to use

rjs = Base_loadRenderJSExtension()
rjs.someFunction()
rjs.someOtherFunction()

instead of something like

Base_rjsExtensionSomeFunction()
Base_rjsExtensionSomeOtherFunction()

which is much less user-friendly. If there is a better alternative I am not aware of, please comment. Also if anything else is amiss.