* Adding base styles for collapsed nav menu.
* Handling varying behaviour on mobile-sized screens, with the menu overlaying content instead of shrinking the content area.
* Folding the menu by default on screen sizes less than 960px, and if that condition is met after an orientation change
* Refactoring logic from Header/index.js to flag if user has scrolled to apply shadow to folded navigation as well.
* Refactoring styles in navigation feature to allow them to be loaded properly with webpack (with imports/etc).
Chi-Hsuan Huang
Joel Thiessen