Added the 'Extend charts and graphs' code sprint in English and French.
Fixed button CSS for 'Extend charts and graphs' code sprint in English and French.
Translated the links for the 'Extend charts and graphs' code sprint.
Merge remote-tracking branch 'upstream/gh-pages' into gh-pages
Merge pull request #60 from thomasgohard/gh-pages

Added the 'Extend charts and graphs' code sprint in English and French