Csslint rake task can read files with underscore

It allows files like: enhanced_fixed and avoid partials like _social_links
Change default button style to grey
Merge branch 'allow-underscores'
Prefix layout component links with main_app

This allows engines to use the app layout
Merge branch 'main_app-prefixes'
Merge pull request #313 from moneyadviceservice/button_styles

Change default button style to grey
Rename yield :scripts to :javascripts