Using normalize-css from bower instead using local file

- Adding normalize-css as devDependencies in bower.json
- Change normalize-css in style.css from local files to bower path
Remove $screen-wide media-queries

$screen-wide is almost never used, so remove it would cause no harm
Change @media-queries rule for mobile grid

Mobile grid (class="grid-xs-") was using max-width rule. Changed to min-width
rule to maintain consistency with other grid class