Correction ugly french.
Added new pages.
Elevator Pitch - Project Owner
Adapt menu translations.
Add get started with distributions.
Symfony explained to a developer.
Begin of translation for get_started/download.html.twig.
Add and translation for what_is_symfony/elevator_pitches/explained_to_a_project_manager.html.twig.
Typo fix.
Translation for GetStarted/download page.
Elevator pitches ended.
Ten criteria translated.
Translation for why_use_a_framework.
when_use_a_framework translated.
Merge pull request #186 from viviengaetan/fr_correction_and_newpages

[wip] [fr] french translation