added missing body tag to default layout
assets for responsive nav added.
css for responsive menu
integrated responsive nav
replace some vendor prefixes with compass mixins
integrated menu css from main.css with _menu.css
fixed padding
header position is only fixed on non-mobile now
fixed typo
added icon size 48px
changed icon. renamed menu wrapper.
fine-tuning for responsive menu.
changed display of logo in 2 different sizes for
mobile and large displays.
added max-width for hero-headings to remove small
border on mobile screens.
replaced background of menu items with border.
(only for mobile displays)
removed border on menu items on large displays.
Merge branch 'responsive-nav' into website

Conflicts:
	_assets/stylesheets/app.css.sass