move master.css into web.scss
restructure location of css files

- move web.css to Root component
- move master.css into web.css
- add support for cssClass in Master.tpl and add support for Master.css (with .cssClass)
port theme to new css file structure
Merge branch 'themes' into simplify-mastercss
adapt themes to new css file structure
translate comment
Merge branch 'simplify-mastercss'