Compile SASS using node-sass

closes #5
- Added node-sass to package.json
- Added new grunt tasks to compile sass and copy fonts/css to dist
- Added new folders to .gitignore
- Added clean task
- Fixed README

ghost/admin/README.md

@@ -79,7 +79,7 @@ Ghost-UI uses [Grunt](http://gruntjs.com/) with convenient methods for working w
 From the command line:
 
 1. Install `grunt-cli` globally with `npm install -g grunt-cli`.
-2. Navigate to the root `/bootstrap` directory, then run `npm install`. npm will look at [package.json](https://github.com/twbs/bootstrap/blob/master/package.json) and automatically install the necessary local dependencies listed there.
+2. Navigate to the root `/Ghost-UI` directory, then run `npm install`. npm will look at [package.json](https://github.com/TryGhost/Ghost-UI/blob/master/package.json) and automatically install the necessary local dependencies listed there.
 
 When completed, you'll be able to run the various Grunt commands provided from the command line.
 

ghost/admin/assets/sass/screen.scss

@@ -52,5 +52,3 @@
         @import "layouts/users";
         /* The users pane. */
 
-        @import "layouts/plugins";
-        /* The plugins pane. */