Improve directory structure

Improve directory structure organization. Fixes #20.

Status: **Opened for visibility**
Reviewers: @kpeatt @jeffkamo

## Notes

- This should wait until #6 and #10 are merged.

## Changes

- Give each component and util its own directory, so future components can bundle other assets (js, dust, etc.)
- Remove top-level components and utils directories
- Update imports and use a Sass load path
- Add some organization to the test directory