Integrate improvements from the French version of the book

* Some layout changes to put more importance on sidebar title
  compared to the pre-title
* Drop some useless section headings
* Lots of small improvements in the French translation
fr-FR: Integrate typo fixes from Cascador

And fix the path for yum repository files in the English string
as well as all the translations.
it-IT: Updated translation of chapters 00a, 00b, 06 and 09 for wheezy
Drop sidebar about buggy lxc-debian template script

The template script has been fixed in Debian 7.4 with
lxc 0.8.0~rc1-8+deb7u2.
it-IT: Updated translation of chapter 03 thanks to Daniele Forsì

Fixes to 06_apt.po file.
Improve build/build-pdf script to not add a duplicate lang attribute

Old versions of Publican do not add the lang attribute that dblatex
needs so we were adding it in the script. Now, newer versions do, so we
should only add it if it's not there yet.
pt-BR: Translated using Weblate.
pt-BR: Translated using Weblate.
pt-BR: Markup fixes so that HTML/ePub build works
Fix output in a sample in the short remedial course

Reported-by: Claudio Filho <filhocf@gmail.com>
pt-BR: update README file
Move page numbers further inwards to avoid problems with some print-on-demand services
pt-BR: Translated using Weblate.
pt-BR: Translated using Weblate.
pt-BR: Translated using Weblate.
pt-BR: Translated using Weblate.
pt-BR: Translated using Weblate.
pt-BR: Translated using Weblate.
pt-BR: Translated using Weblate.
pt-BR: Translated using Weblate.