Defining variants in the Carbon React library

[aagonzales]

With the new definition of variant, we need to make sure our docs and index organization accurately aligns to the new categories.

Deliverable: https://ibm.box.com/s/4rwr6yn0hgh5ujirn0ij18hhr8mu3h1s

• Complete list in box note to determine final roll-up status
• Review and agree upon categorization and roll
• Clear definition of what is a "type" in a component with no roll-up and a component variant that is shown individually in the index.
• Open issue to clean up documentation on the Carbon website to match

Note: consider changes to Storybook organization. This will need a separate dev issue when box note work is complete.

[mattrosno]

@aagonzales I set a dependency and epic for this issue.