Filename is split as an URL path, and joined in OS-dependent manner.
Remove corresponding comment in all buildout.hash.cfg files.

This is a follow-up of commit 5c980caf,
now that the new code of the 'wrapper' recipe is used (1.0.58 released).

In all examples of custom.js the Jupyter variable is capitalized, but
here it was not. Because of unknown reason, without Jupyter upgrade,
it stopped to working. Switching from "jupyter" to "Jupyter" fixes the
problem.

 zc.buildout version up to 2.5.2+slapos012
 slapos.recipe.template version up to 4.3
 slapos.core version up to 1.4.4

numpy  >= 1.13.1 is required for numpy.core.multiarray

Keep url in publish parameters, as it is used by other requests.

JupyterLab is provided side-by-side with Jupyter Classic interface with same process.

Published URL changed:

 * jupyterlab-url provides IPv6 URL to JupterLab interface
 * jupyter-class-url provides IPv6 URL to the classic UI

Thanks to using only one process, the path in the URL differentiates the style of the interface.

Note: This MR replaces closed !207

/reviewed-on !218

@Tyagov  @luke 

/reviewed-on !212

Instead of templating python code, make it static and parameterize it
with parameters.

kernel.json can pass default ERP5 url, which is (dirty) read by
ERP5kernel. Additionally ERP5kernel.py is just linked into kernel
directory, which simplifies debugging.

Note: This commit is still dirty, but it prepares ERP5kernel.py to be
      packaged, thus there is no reason to make more changes and
      cleanup.

/reviewed-on !206