style(main.scss): put import at top
feat(divider): add implementation of the divider component

This commit adds an implementation of the "divider" component which groups and separates content within lists and page layouts using strong visual and spatial distinctions. Demos and docs accompany the implementation.

Closes #194. Closes #250.
docs(): add material-item-content to api items
demo(toolbar): add material-item-content
style(colors): remove unused color-text-* variables for now