Build: Concat IE8 assets and align markup

Create vapour-ie8.js that includes all IE8 polyfills and Vapour loader
- Remove Excanvas since it is concated for IE8 only
- Use more up-to-date HTML5 Shiv
- Update markup for IE8 only backwards support
Merge pull request #3241 from wet-boew/3240-fixup

Build: Concat IE8 assets and align markup