`py--unfontify-banner' IPython again

unfontify first paragraph
Testing py-shell lp:1398530
Testing py-shell lp:1398530, again
As there are of couple of things differently at Python and IPyhton
shells, let's have different shell modes:

Instead of `py-shell-mode' now
`py-python-shell-mode' resp. `py-ipython-shell-mode'
Run `py--run-unfontify-timer' just once

timer issues fixed
(I)Python setup made more reliable

Provide derived modes `py-python-shell-mode-map', `py-ipython-shell-mode-map'

reads IPython.__version__
from IPython-shell created
not default executable by shell-script

`py--execute-buffer-finally' fixed, `py-exception-buffer'
`py--postprocess-comint' fixed
Docu updated
opening-brace-on-builtins-lp-1400951-test added