Revised header elements & styling and reorganized Sass files for easier maintenance.
Renamed: _defaults.scss -> _elements.scss
Renamed: _settings.scss -> _defaults.scss (default values *)
Renamed: _site.scss -> _custom.scss
Added: _settings.scss - theme setting values (override defaults)
(* - added !default to Foundation setting default values)
Revised app.scss import statements accordingly.
Disable theme colour customizer