[Python-modules-team] Bug#943901: ipykernel python 3.8

[Gordon Ball]

I've forked the source package for ipykernel to retain (for now) the
python2 version.

(Rationale: while there aren't rdeps, keeping this package is needed to
keep the ability to use python2 jupyter notebook. This package is
flagged py2keep; I don't think dropping python2 here frees up many other
rdeps until and unless ipython2 can be dropped).

The forked source package (ipykernel-py2) has been sitting in NEW since
2019-11-17. In principle dropping python2 from this source package
doesn't have to wait for it to be accepted, but I preferred to maintain
continuity.