[scss] Separate Font Awesome icons.
[scss] Separate Google colour palette.
[scss] Separate fonts.
[scss] Separate common model styling.
[scss] Separate sizes and root model styling.

The latter necessitated the former.
[scss] Separate toolbar and semantic colours.

The former necessitated the latter, this time.
[scss] Separate play states, remove @dark-text.
[scss] Separate load states.
[scss] Separate item types.
[scss] Use each loop for roots.
[scss] Use each loop for sets.
[scss] Separate model sets.
[scss] Separate nav links.
[scss] Refactor nav links.
[scss] Separate JSON console theming.
[scss] Remove legend theming.
[scss] Remove @border mixin.
[scss] Move playlist styling to model-styles-sets.
[scss] Move constant margin override.
[scss] Move rest of styling out of screen.scss.

This more or less concludes the SCSS refactoring.