Remove Google Frame message

As said at http://blog.chromium.org/2013/06/retiring-chrome-frame.html Google Frame was retired/obsolete.

Changed "chromeframe" class to "browsehappy"
Add vertical centering for audio-, canvas- and video-tags

Remove the gap between videos, audio and canvas and the bottom of
their containers by vertically centering the tags.

Closes #1326.
Remove Chrome Frame meta tag and HTTP header hints

See also `Retiring Chrome Frame - developer FAQ`:
https://developers.google.com/chrome/chrome-frame/

Close #1396.
Merge pull request #1 from h5bp/master

Chrome frame and vertical centering