Add backtotop.css
Add backtotop.js
Add back to top button.
Add back to top button to rindex.html
Add back to top button to library.html
Merge branch 'master' of https://github.com/POOSDFall2014/FlixBook-FrontEnd
Merge branch 'master' of https://github.com/POOSDFall2014/FlixBook-FrontEnd