[README] improve contribution section with links and command examples

[README] point to logilab's jenkins in tests section

[pyramid] improve pyramid warning with link to doc on how to write pyramid.ini file

[doc] translate french to english

[doc] typo, 'CW' doesn't exist in the example

[doc] always indicate the file in which the code should be put

[doc] respect pep8 in code examples

[doc] serie a small improvments

[doc] typo, the field is "name" not "title"

[doc] fix, command "create" is missing base cube

[doc] improve blog tutorial first steps and explain common errors

[doc] how to install pyramid or twisted application server

[doc] new behavior in virtualenv since 3.26

[skeleton] use python3 flake8 In tox "flake8" environment, use python 3 virtualenv, so we can check for python3 incompatible syntax.

[skeleton] drop whitelist_externals for flake8 whitelist_externals makes sense when used with sitepackages=true. In this case it will always rely on $VIRTUAL_ENV/bin/flake8 so, the whitelist_externals has no effect.