add ie css switch to layout templates

This PR adds various ie css tags to the html tag based on the css browser switch mentioned in https://github.com/owncloud/core/issues/308#issuecomment-13583610

It lays the foundation to clean up the css in future pull requests.

It will then be possible to cleanly separate ie CSS magic from HTML5 by prepending rules with .ie, .ie7 or .lte9

Instead of using a browser switch to include a special ie CSS file in the header this allows us to keep related css in one place / file. This hopefully prevents regressions for CSS issues like in #1779 

@karlitschek @Raydiation @jancborchardt @tanghus @bartv2 @DeepDiver1975 please vote