chore(website): Update the website to bootstrap 3.1 and make it working on mobile devices

- Make the site web responsive to works on mobile devices.
- Add meta tag viewport
- Update the download modal & remove the modal backdrop
- Update the popovers in html and JS files
- Remove the video modal and embed videos in the pages
- Update Bootstrap to 3.1.0
- Update Font Awesome to 4.0.3
- Use CDN for faster loading
- Update the copyright to 2014
- Clean up