Add styles for breadcrumbs component

[HaSistrunk]

Fixes issue #56

• Adapts rockarch.org breadcrumb styles
• Removes context-specific margin-bottom value that adds space around the component.
• Adds comments to better document CSS blocks.
• Remove styles on navigation element and apply to ol instead. This has been documented in the change tracking document.

[helrond]

I was a little unsure how to approach the .breadcrumbs ol styles that specify responsive changes depending on screen size. Currently, rockarch.org is the only one of our sites that uses breadcrumbs, but I'm not sure that those should be baked into the component. Perhaps this is something to consider later on in relation to issue #4 .

I also feel like these styles don't belong in the component - they're really layout-specific.

Thinking about this, I'm wondering if we should completely do away with the notion of styled wrapping nav, and instead put the breadcrumbs class on the ol itself. I think the full-width layout stuff and background color are probably not universal, and should be considered part of a layout container that the breadcrumbs component sits in. How does that sound?

[HaSistrunk]

Thinking about this, I'm wondering if we should completely do away with the notion of styled wrapping nav, and instead put the breadcrumbs class on the ol itself. I think the full-width layout stuff and background color are probably not universal, and should be considered part of a layout container that the breadcrumbs component sits in. How does that sound?

Yeah, that approach makes a lot of sense to me. We might actually consider creating a container component in the future.