SASS file reorganization

Some important file name changes. The SASS stylesheets have been renamed as follows:
* _settings.scss - for style variables
* _style.scss - for application styles
* foundation-skin.scss - for the composite foundation + application stylesheet

A seperate _theme.scss has been created in a subfolder for each theme to override the style settings. eg. the metastudio theme will reside in ```scss/metastudio/_theme.scss```