Remove unnecessary media query prefix "all and "

For example, instead of "@media all and (min-width: 40em)" just use
"@media (min-width: 40em)". This is valid according to the W3C Media
Queries specification: http://www.w3.org/TR/css3-mediaqueries/
Merge pull request #28 from Steffen185/issue-23-v2

Remove unnecessary media query prefix "all and " (updated)