Reworked index.html

- Added `lang` attribute to `html` tag
- Replaced old charset meta tag with the new one
- Moved viewport meta tag further to the top to be recognized early
- Removed IE render engine meta tag (no longer needed)
- Commented out description meta tag while it's empty (TO DO!)
- Added HTML5 shiv to enable HTML5 support for <IE9
- Changed _browse happy_ notification to show on <IE9 instead of <IE8

__TO DO:__

- Add Google Analytics ID
- Add favicon.ico (or other shortcut icon file)