add brand for homepage nav
add mini-player for marketing
use github frontpage color and style
home sigup, nice and simple
rm twitter css
categories
github footer
lynda.com style course partial
add about pages #48
Merge pull request #50 from luckyyang/about_page

About page
Merge branch 'mini-player' into tmp

Conflicts:
	app/assets/stylesheets/application.css.scss.erb
course partail design, #51
about page #48
click the poster and u get the preview video
color scheme
modify about pages, some words #48