Reorganization

# Changes
 - Organizes patterns into components, modules, and regions.
 - Improved scroll indicator performance (throttled; more efficient finding which element to highlight).
 - Removed unused `.embed-container` pattern (duplicate of `.media-video`).

For review: @DoSomething/front-end

What's the 40px? Some extra padding or calculated from margin of an item? Would it be useful to dynamically calculate that off of the item in case it changes in the future? Just a thought; not sure....