Add HTML/CSS post-processing, general improvements

[jgautheron]

• Add post processing for HTML/CSS files, the production files are now located under /dist
• Optimize images
• Fix issue with Firefox Mobile (media queries were not executed)
• Layout improvements

@grvgr Is there something to change in the deployment scripts since the web folder changed? @realrasengan I removed some spaces in the homepage brands   so that they look vertically centered, let me know if that works out for you!

[jgautheron]

@grvgr I added the build system to simplify our lives and to set us up with a flexible boilerplate for the future. 1/ Performance matters and we need to minify and optimize the code and assets. 2/ The less code we have the better, and for that we have an autoprefixer that lets us write stylesheets without vendor prefixes but will add them afterwards. Also if any of us makes change in the stylesheet, the browser compatibility will be at minima covered by prefixes. 3/ Eventually I'd like to add a system of partials to make the HTML code DRYer. Currently if we change the menu we have to change it in as many pages we have, which is unpractical but worse, error-prone.